Publications by authors named "Daniel Paik"

17 Publications

  • Page 1 of 1

Anti-viral protective capacity of tissue resident memory T cells.

Curr Opin Virol 2021 02 30;46:20-26. Epub 2020 Oct 30.

Columbia Center for Translational Immunology, Columbia University Medical Center, New York, NY 10032, United States; Department of Microbiology and Immunology, Columbia University Medical Center, New York, NY 10032, United States; Department of Surgery, Columbia University Medical Center, New York, NY 10032, United States. Electronic address:

It has become increasingly clear that a subset of T cells which persist at diverse infection sites, known as tissue-resident memory T cells (T), can mediate efficacious protective immunity against many types of viral infections. Recent studies have elucidated the mechanisms by which T coordinate enhanced viral clearance in different sites through rapid production of effector cytokines and cytolytic mediators, in situ expansion, differentiation to circulating effector cells, and immune cell recruitment. This tissue-localized response also includes enhancement at the local lymphoid sites which contribute to fortifying T-mediated protection. Understanding how these responses occur in a tissue-wide context will provide key insights for development of vaccines and therapeutics.
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http://dx.doi.org/10.1016/j.coviro.2020.09.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7979430PMC
February 2021

Influenza infection fortifies local lymph nodes to promote lung-resident heterosubtypic immunity.

J Exp Med 2021 Jan;218(1)

Department of Microbiology and Immunology, Columbia University Medical Center, New York, NY.

Influenza infection generates tissue-resident memory T cells (TRMs) that are maintained in the lung and can mediate protective immunity to heterologous influenza strains, but the precise mechanisms of local T cell-mediated protection are not well understood. In a murine heterosubtypic influenza challenge model, we demonstrate that protective lung T cell responses derive from both in situ activation of TRMs and the enhanced generation of effector T cells from the local lung draining mediastinal lymph nodes (medLNs). Primary infection fortified the medLNs with an increased number of conventional dendritic cells (cDCs) that mediate enhanced priming of T cells, including those specific for newly encountered epitopes; cDC depletion during the recall response diminished medLN T cell generation and heterosubtypic immunity. Our study shows that during a protective recall response, cDCs in a fortified LN environment enhance the breadth, generation, and tissue migration of effector T cells to augment lung TRM responses.
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http://dx.doi.org/10.1084/jem.20200218DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7534905PMC
January 2021

Real-time Doppler ultrasound to identify vessels and guide needle placement for gynecologic interstitial brachytherapy.

Brachytherapy 2018 Sep - Oct;17(5):742-746. Epub 2018 May 31.

Department of Radiation, John Muir Health, Walnut Creek, CA.

Purpose: Doppler ultrasound (US) gives real-time information regarding anatomy and blood vessel location to guide needle placement for gynecologic interstitial (IS) brachytherapy (BT). We retrospectively assessed Doppler US images for vessel quantity, size, and distribution in cervical cancer patients undergoing high-dose-rate BT at our institution.

Methods And Materials: Eleven consecutive patients undergoing IS high-dose-rate BT implants for cervical cancer between 2015 and 2017 were included. Transrectal Doppler US was used for real-time image guidance. US images were retrospectively evaluated. Vessel quantity, size, and distribution at superior and inferior levels of the cervix were recorded. Correlation of vessel quantity with tumor size and International Federation of Gynecology and Obstetrics stage was evaluated.

Results: Average vessel quantity was 4.2 in the inferior cervix and 3.8 in the superior cervix (range 1-11). Median vessel diameter was 2 mm in the inferior cervix and 2 mm in the superior cervix (range 1-6 mm). The most common location was posterolateral (3:00-5:00 and 7:00-9:00), outer third (78% of vessels inferiorly, 64% of vessels superiorly). Vessel quantity was correlated to initial tumor size superiorly (p = 0.04, paired t-test) but not inferiorly (p = 0.31, paired t-test). There was no correlation between vessel quantity and International Federation of Gynecology and Obstetrics stage (p > 0.05, analysis of variance). Doppler US was successfully used to guide needle placement away from visualized blood vessels with no incidents of hemorrhage in these patients.

Conclusions: Doppler US is a useful tool to guide needle placement for IS BT for cervical cancer. Vessel quantity varied with increased vessel quantity seen higher in the cervix for larger tumors. Vessels were most commonly distributed in the outer third of the posterolateral cervix.
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http://dx.doi.org/10.1016/j.brachy.2018.04.006DOI Listing
March 2019

Biased Generation and In Situ Activation of Lung Tissue-Resident Memory CD4 T Cells in the Pathogenesis of Allergic Asthma.

J Immunol 2018 03 17;200(5):1561-1569. Epub 2018 Jan 17.

Columbia Center for Translational Immunology, Columbia University Medical Center, New York, NY 10032;

Asthma is a chronic inflammatory disease mediated by allergen-specific CD4 T cells that promote lung inflammation through recruitment of cellular effectors into the lung. A subset of lung T cells can persist as tissue-resident memory T cells (TRMs) following infection and allergen induction, although the generation and role of TRM in asthma persistence and pathogenesis remain unclear. In this study, we used a mouse model of chronic exposure to intranasal house dust mite (HDM) extract to dissect how lung TRMs are generated and function in the persistence and pathogenesis of allergic airway disease. We demonstrate that both CD4 and CD8 T cells infiltrate into the lung tissue during acute HDM exposure; however, only CD4 TRMs, and not CD8 TRMs, persist long term following cessation of HDM administration. Lung CD4 TRMs are localized around airways and are rapidly reactivated upon allergen re-exposure accompanied by the rapid induction of airway hyperresponsiveness independent of circulating T cells. Lung CD4 TRM activation to HDM challenge is also accompanied by increased recruitment and activation of dendritic cells in the lungs. Our results indicate that lung CD4 TRMs can perpetuate allergen-specific sensitization and direct early inflammatory signals that promote rapid lung pathology, suggesting that targeting lung CD4 TRMs could have therapeutic benefit in alleviating recurrent asthma episodes.
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http://dx.doi.org/10.4049/jimmunol.1700257DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5821590PMC
March 2018

Spindle Assembly and Chromosome Segregation Requires Central Spindle Proteins in Drosophila Oocytes.

Genetics 2016 Jan 12;202(1):61-75. Epub 2015 Nov 12.

Waksman Institute, Rutgers, The State University of New Jersey, New Jersey 08854 Department of Genetics, Rutgers, The State University of New Jersey, New Jersey 08854

Oocytes segregate chromosomes in the absence of centrosomes. In this situation, the chromosomes direct spindle assembly. It is still unclear in this system which factors are required for homologous chromosome bi-orientation and spindle assembly. The Drosophila kinesin-6 protein Subito, although nonessential for mitotic spindle assembly, is required to organize a bipolar meiotic spindle and chromosome bi-orientation in oocytes. Along with the chromosomal passenger complex (CPC), Subito is an important part of the metaphase I central spindle. In this study we have conducted genetic screens to identify genes that interact with subito or the CPC component Incenp. In addition, the meiotic mutant phenotype for some of the genes identified in these screens were characterized. We show, in part through the use of a heat-shock-inducible system, that the Centralspindlin component RacGAP50C and downstream regulators of cytokinesis Rho1, Sticky, and RhoGEF2 are required for homologous chromosome bi-orientation in metaphase I oocytes. This suggests a novel function for proteins normally involved in mitotic cell division in the regulation of microtubule-chromosome interactions. We also show that the kinetochore protein, Polo kinase, is required for maintaining chromosome alignment and spindle organization in metaphase I oocytes. In combination our results support a model where the meiotic central spindle and associated proteins are essential for acentrosomal chromosome segregation.
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http://dx.doi.org/10.1534/genetics.115.181081DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4701103PMC
January 2016

Breast cancer following ovarian cancer in BRCA mutation carriers.

JAMA Surg 2014 Dec;149(12):1306-13

Division of Surgical Oncology, Department of Surgery, Cedars-Sinai Medical Center, Los Angeles, California.

Importance: BRCA mutation carriers are at increased risk of developing breast cancer. However, the incidence of breast cancer after a diagnosis of epithelial ovarian cancer (EOC), one of the tubal/peritoneal cancers collectively referred to as pelvic serous carcinomas, is not well known. Optimal breast cancer surveillance and detection for these patients have also not been well characterized.

Objectives: To determine the incidence of breast cancer after a diagnosis of EOC and to evaluate the need for breast cancer surveillance for these patients.

Design, Setting, And Participants: A retrospective database review of 364 patients who underwent BRCA mutation testing for EOC (stages I-IV) between 1998 and 2012 at an academic medical center with gynecologic and breast cancer centers.

Main Outcomes And Measures: Incidence of breast cancer and methods of surveillance.

Results: Of 364 patients, 135 (37.1%) were found to carry a germline BRCA1 or BRCA2 mutation. The mean age of patients at diagnosis of EOC was 49.5 years (range, 28-89 years). Of the 135 patients, 12 (8.9%) developed breast cancer. The median time from diagnosis of EOC to diagnosis of breast cancer was 50.5 months. Annual mammography was performed for 80 patients (59.3%), with annual magnetic resonance imaging of the breasts performed for 60 patients (44.4%). Thirteen patients (9.6%) underwent a bilateral prophylactic mastectomy at a median of 23 months following EOC diagnosis. Breast cancer was most commonly diagnosed by mammography for 7 of the 12 patients (58.3%), 3 (25.0%) of whom had a palpable mass and 2 (16.7%) of whom had incidental breast cancer detected during a prophylactic mastectomy. Seven patients with breast cancer (58.3%) underwent a bilateral mastectomy. All patients had early-stage breast cancer (stages 0-II). Four patients (33.3%) received adjuvant chemotherapy. At a median follow-up of 6.3 years, 4 of the 12 patients (33.3%) died of recurrent EOC after a diagnosis of breast cancer. The overall 10-year survival rate for the entire cohort of 135 patients was 17.0%.

Conclusions And Relevance: The risk of metachronous breast cancer is low in patients with known BRCA mutations and EOC. A majority of these cases of breast cancer at an early stage are detected by use of mammography. Despite the small number of patients in our study, these results suggest that optimal breast cancer surveillance for patients with BRCA-associated EOC needs to be reevaluated given the low incidence of breast cancer among these high-risk patients. Confirmation of our findings from larger studies seems to be indicated.
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http://dx.doi.org/10.1001/jamasurg.2014.1081DOI Listing
December 2014

Low levels of circulating estrogen sensitize PTEN-null endometrial tumors to PARP inhibition in vivo.

Mol Cancer Ther 2013 Dec 12;12(12):2917-28. Epub 2013 Nov 12.

Corresponding Author: Sanaz Memarzadeh, University of California, Los Angeles, 555 Westwood Plaza, Level B, Box 957243, 1015 Terasaki Life Sciences Building, Los Angeles, CA 90095.

Earlier in vitro work demonstrated that PARP inhibition induces cell death in PTEN-null endometrial cancer cell lines, but the in vivo therapeutic efficacy of these agents against endometrial cancer remains unknown. Here, we test the efficacy of AZD2281 (olaparib), an oral PARP inhibitor, in the therapy of PTEN-null endometrial tumors in a preclinical endometrial cancer mouse model. Primary endometrial tumors were generated by epithelial loss of PTEN using an in vivo model. This model recapitulates epithelial-specific loss of PTEN seen in human tumors, and histologically resembles endometrioid carcinomas, the predominant subtype of human endometrial cancers. Olaparib was administered orally to tumor-bearing mice in two hormonal extremes: high or low estrogen. Olaparib treatment achieved a significant reduction in tumor size in a low estrogenic milieu. In striking contrast, no response to olaparib was seen in tumors exposed to high levels of estrogen. Two key observations were made when estrogen levels were dropped: (i) the serum concentration of olaparib was significantly increased, resulting in sustained PARP inhibition at the tumor bed; and (ii) the homologous recombination pathway was compromised, as evidenced by decreased Rad51 protein expression and function. These two mechanisms may account for the sensitization of PTEN-null tumors to olaparib with estrogen deprivation. Results of this preclinical trial suggest that orally administered PARP inhibitors in a low estrogenic hormonal milieu can effectively target PTEN-null endometrial tumors. Extension of this work to clinical trials could personalize the therapy of women afflicted with advanced endometrial cancer using well-tolerated orally administered therapeutic agents.
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http://dx.doi.org/10.1158/1535-7163.MCT-13-0572DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3904550PMC
December 2013

Progesterone receptor signaling in the microenvironment of endometrial cancer influences its response to hormonal therapy.

Cancer Res 2013 Aug 6;73(15):4697-710. Epub 2013 Jun 6.

Departments of Obstetrics and Gynecology, Molecular and Medical Pharmacology, and Molecular, Cell and Developmental Biology, David Geffen School of Medicine, Los Angeles, USA.

Progesterone, an agonist for the progesterone receptor (PR), can be an efficacious and well-tolerated treatment in endometrial cancer. The clinical use of progesterone is limited because of the lack of biomarkers that predict hormone sensitivity. Despite its efficacy in cancer therapy, mechanisms and site of action for progesterone remain unknown. Using an in vivo endometrial cancer mouse model driven by clinically relevant genetic changes but dichotomous responses to hormonal therapy, we show that signaling through stromal PR is necessary and sufficient for progesterone antitumor effects. Endometrial cancers resulting from epithelial loss of PTEN (PTENKO) were hormone sensitive and had abundant expression of stromal PR. Stromal deletion of PR as a single genetic change in these tumors induced progesterone resistance indicating that paracrine signaling through the stroma is essential for the progesterone therapeutic effects. A hormone-refractory endometrial tumor with low levels of stromal PR developed when activation of KRAS was coupled with PTEN-loss (PTENKO/Kras). The innate progesterone resistance in PTENKO/Kras tumors stemmed from methylation of PR in the tumor microenvironment. Add-back of stromal PR expressed from a constitutively active promoter sensitized these tumors to progesterone therapy. Results show that signaling through stromal PR is sufficient for inducing hormone responsiveness. Our findings suggest that epigenetic derepression of stromal PR could be a potential therapeutic target for sensitizing hormone-refractory endometrial tumors to progesterone therapy. On the basis of these results, stromal expression of PR may emerge as a reliable biomarker in predicting response to hormonal therapy.
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http://dx.doi.org/10.1158/0008-5472.CAN-13-0930DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3752407PMC
August 2013

Estrogen and progesterone together expand murine endometrial epithelial progenitor cells.

Stem Cells 2013 Apr;31(4):808-22

Department of Obstetrics and Gynecology, University of California, Los Angeles, California, USA.

Synchronous with massive shifts in reproductive hormones, the uterus and its lining the endometrium expand to accommodate a growing fetus during pregnancy. In the absence of an embryo the endometrium, composed of epithelium and stroma, undergoes numerous hormonally regulated cycles of breakdown and regeneration. The hormonally mediated regenerative capacity of the endometrium suggests that signals that govern the growth of endometrial progenitors must be regulated by estrogen and progesterone. Here, we report an antigenic profile for isolation of mouse endometrial epithelial progenitors. These cells are EpCAM(+) CD44(+) ITGA6(hi) Thy1(-) PECAM1(-) PTPRC(-) Ter119(-), comprise a minor subpopulation of total endometrial epithelia and possess a gene expression profile that is unique and different from other cells of the endometrium. The epithelial progenitors of the endometrium could regenerate in vivo, undergo multilineage differentiation and proliferate. We show that the number of endometrial epithelial progenitors is regulated by reproductive hormones. Coadministration of estrogen and progesterone dramatically expanded the endometrial epithelial progenitor cell pool. This effect was not observed when estrogen or progesterone was administered alone. Despite the remarkable sensitivity to hormonal signals, endometrial epithelial progenitors do not express estrogen or progesterone receptors. Therefore, their hormonal regulation must be mediated through paracrine signals resulting from binding of steroid hormones to the progenitor cell niche. Discovery of signaling defects in endometrial epithelial progenitors or their niche can lead to development of better therapies in diseases of the endometrium.
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http://dx.doi.org/10.1002/stem.1337DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3774116PMC
April 2013

Stem-like epithelial cells are concentrated in the distal end of the fallopian tube: a site for injury and serous cancer initiation.

Stem Cells 2012 Nov;30(11):2487-97

Department of Obstetrics and Gynecology, David Geffen School of Medicine, University of California, Los Angeles, California, USA.

The reproductive role of the fallopian tube is to transport the sperm and egg. The tube is positioned to act as a bridge between the ovary where the egg is released and the uterus where implantation occurs. Throughout reproductive years, the fallopian tube epithelium undergoes repetitive damage and regeneration. Although a reservoir of adult epithelial stem cells must exist to replenish damaged cells, they remain unidentified. Here, we report isolation of a subset of basally located human fallopian tube epithelia (FTE) that lack markers of ciliated (β-tubulin; TUBB4) or secretory (PAX8) differentiated cells. These undifferentiated cells expressed cell surface antigens: epithelial cell adhesion molecule, CD44, and integrin α 6. This FTE subpopulation was fivefold enriched for cells capable of clonal growth and self-renewal suggesting that they contain the FTE stem-like cells (FTESCs). A twofold enrichment of the FTESC was found in the distal compared to the proximal end of the tube. The distal fimbriated end of the fallopian tube is a well-characterized locus for initiation of serous carcinomas. An expansion of the cells expressing markers of FTESC was detected in tubal intraepithelial carcinomas and in fallopian tubes from patients with invasive serous cancer. These findings suggest that FTESC may play a role in the initiation of serous tumors. Characterization of these stem-like cells will provide new insight into how the FTE regenerate, respond to injury, and may initiate cancer.
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http://dx.doi.org/10.1002/stem.1207DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4442093PMC
November 2012

Osteoconductive protamine-based polyelectrolyte multilayer functionalized surfaces.

Biomaterials 2011 Oct 18;32(30):7491-502. Epub 2011 Jul 18.

Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

The integration of orthopedic implants with host bone presents a major challenge in joint arthroplasty, spinal fusion and tumor reconstruction. The cellular microenvironment can be programmed via implant surface functionalization allowing direct modulation of osteoblast adhesion, proliferation, and differentiation at the implant--bone interface. The development of layer-by-layer assembled polyelectrolyte multilayer (PEM) architectures has greatly expanded our ability to fabricate intricate nanometer to micron scale thin film coatings that conform to complex implant geometries. The in vivo therapeutic efficacy of thin PEM implant coatings for numerous biomedical applications has previously been reported. We have fabricated protamine-based PEM thin films that support the long-term proliferation and differentiation of pre-osteoblast cells on non-cross-linked film-coated surfaces. These hydrophilic PEM functionalized surfaces with nanometer-scale roughness facilitated increased deposition of calcified matrix by osteoblasts in vitro, and thus offer the potential to enhance implant integration with host bone. The coatings can make an immediate impact in the osteogenic culture of stem cells and assessment of the osteogenic potential of new therapeutic factors.
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http://dx.doi.org/10.1016/j.biomaterials.2011.06.032DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3218099PMC
October 2011

Common variants at 19p13 are associated with susceptibility to ovarian cancer.

Nat Genet 2010 Oct 19;42(10):880-4. Epub 2010 Sep 19.

Department of Oncology, University of Cambridge, Cambridge, UK.

Epithelial ovarian cancer (EOC) is the leading cause of death from gynecological malignancy in the developed world, accounting for 4% of the deaths from cancer in women. We performed a three-phase genome-wide association study of EOC survival in 8,951 individuals with EOC (cases) with available survival time data and a parallel association analysis of EOC susceptibility. Two SNPs at 19p13.11, rs8170 and rs2363956, showed evidence of association with survival (overall P = 5 × 10⁻⁴ and P = 6 × 10⁻⁴, respectively), but they did not replicate in phase 3. However, the same two SNPs demonstrated genome-wide significance for risk of serous EOC (P = 3 × 10⁻⁹ and P = 4 × 10⁻¹¹, respectively). Expression analysis of candidate genes at this locus in ovarian tumors supported a role for the BRCA1-interacting gene C19orf62, also known as MERIT40, which contains rs8170, in EOC development.
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http://dx.doi.org/10.1038/ng.666DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3125495PMC
October 2010

Higher sensitivity to patupilone versus paclitaxel chemotherapy in primary uterine serous papillary carcinoma cell lines with high versus low HER-2/neu expression in vitro.

Gynecol Oncol 2010 Oct 31;119(1):140-5. Epub 2010 Jul 31.

Department of Obstetrics, Gynecology and Reproductive Sciences, Yale University School of Medicine, 333 Cedar Street, PO Box 208063, New Haven, CT 06520-8063, USA.

Objective: To compare the in vitro sensitivity/resistance to patupilone versus paclitaxel in uterine serous papillary carcinoma (USPC) with high versus low HER-2/neu expression.

Methods: Six primary USPC cell lines, half of which overexpress HER-2/neu at a 3+ level, were evaluated for growth rate and tested for their in vitro sensitivity/resistance to patupilone versus paclitaxel by MTS assays. Quantitative RT-PCR was used to identify potential mechanisms underlying the differential sensitivity/resistance to patupilone versus paclitaxel in primary USPC cell lines.

Results: Cell lines overexpressing HER-2/neu showed higher proliferation when compared to low HER-2/neu-expressing cell lines. Compared to low-expressing cell lines, high HER-2/neu expressors were significantly more sensitive to patupilone than to paclitaxel (P<0.0002). In contrast, there was no appreciable difference in sensitivity to patupilone versus paclitaxel in primary USPC cell lines with low HER-2/neu expression. Higher levels of β-tubulin III (TUBB3) and P-glycoprotein (ABCB1) were detected in USPC cell lines with high versus low HER-2/neu expression (P<0.05).

Conclusions: USPC overexpressing HER-2/neu display greater in vitro sensitivity to patupilone and higher levels of the patupilone molecular target TUBB3 when compared to low HER-2/neu expressors. Due to the adverse prognosis associated with HER-2/neu overexpression in USPC patients, patupilone may represent a promising novel drug to combine to platinum compounds in this subset of aggressive endometrial tumors.
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http://dx.doi.org/10.1016/j.ygyno.2010.06.024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2939197PMC
October 2010

Gastroschisis and bladder herniation: case report and literature review.

J Ultrasound Med 2010 Feb;29(2):313-6

Division of Maternal-Fetal Medicine, Yale University, 330 Cedar St, New Haven, CT 06504 USA.

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http://dx.doi.org/10.7863/jum.2010.29.2.313DOI Listing
February 2010

Ultrafast light-induced response of photoactive yellow protein chromophore analogues.

Photochem Photobiol Sci 2007 Jul 18;6(7):780-7. Epub 2007 Apr 18.

UMR CNRS-ENS 8640 PASTEUR, Département de Chimie, Ecole Normale Supérieure, 24 rue Lhomond, 75005, Paris, France.

The fluorescence decays of several analogues of the photoactive yellow protein (PYP) chromophore in aqueous solution have been measured by femtosecond fluorescence up-conversion and the corresponding time-resolved fluorescence spectra have been reconstructed. The native chromophore of PYP is a thioester derivative of p-coumaric acid in its trans deprotonated form. Fluorescence kinetics are reported for a thioester phenyl analogue and for two analogues where the thioester group has been changed to amide and carboxylate groups. The kinetics are compared to those we previously reported for the analogues bearing ketone and ester groups. The fluorescence decays of the full series are found to lie in the 1-10 ps range depending on the electron-acceptor character of the substituent, in good agreement with the excited-state relaxation kinetics extracted from transient absorption measurements. Steady-state photolysis is also examined and found to depend strongly on the nature of the substituent. While it has been shown that the ultrafast light-induced response of the chromophore in PYP is controlled by the properties of the protein nanospace, the present results demonstrate that, in solution, the relaxation dynamics and pathway of the chromophore is controlled by its electron donor-acceptor structure: structures of stronger electron donor-acceptor character lead to faster decays and less photoisomerisation.
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http://dx.doi.org/10.1039/b700927eDOI Listing
July 2007

Ultrafast photoisomerization of photoactive yellow protein chromophore analogues in solution: influence of the protonation state.

Chemphyschem 2006 Aug;7(8):1717-26

UMR CNRS-ENS 8640 Pasteur, Département de Chimie, Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris Cedex 05, France.

We investigate solvent viscosity and polarity effects on the photoisomerization of the protonated and deprotonated forms of two analogues of the photoactive yellow protein (PYP) chromophore. These are trans-p-hydroxybenzylidene acetone and trans-p-hydroxyphenyl cinnamate, studied in solutions of different polarity and viscosity at room temperature, by means of femtosecond fluorescence up-conversion. The fluorescence lifetimes of the protonated forms are found to be barely sensitive to solvent viscosity, and to increase with increasing solvent polarity. In contrast, the fluorescence decays of the deprotonated forms are significantly slowed down in viscous media and accelerated in polar solvents. These results elucidate the dramatic influence of the protonation state of the PYP chromophore analogues on their photoinduced dynamics. The viscosity and polarity effects are, respectively, interpreted in terms of different isomerization coordinates and charge redistribution in S(1). A trans-to-cis isomerization mechanism involving mainly the ethylenic double-bond torsion and/or solvation is proposed for the anionic forms, whereas "concerted" intramolecular motions are proposed for the neutral forms.
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http://dx.doi.org/10.1002/cphc.200600137DOI Listing
August 2006
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