Publications by authors named "Amy Chu"

12 Publications

  • Page 1 of 1

The structural basis of fatty acid elongation by the ELOVL elongases.

Nat Struct Mol Biol 2021 06 10;28(6):512-520. Epub 2021 Jun 10.

Structural Genomics Consortium, Centre for Medicines Discovery, University of Oxford, Oxford, UK.

Very long chain fatty acids (VLCFAs) are essential building blocks for the synthesis of ceramides and sphingolipids. The first step in the fatty acid elongation cycle is catalyzed by the 3-keto acyl-coenzyme A (CoA) synthases (in mammals, ELOVL elongases). Although ELOVLs are implicated in common diseases, including insulin resistance, hepatic steatosis and Parkinson's, their underlying molecular mechanisms are unknown. Here we report the structure of the human ELOVL7 elongase, which comprises an inverted transmembrane barrel surrounding a 35-Å long tunnel containing a covalently attached product analogue. The structure reveals the substrate-binding sites in the narrow tunnel and an active site deep in the membrane. We demonstrate that chain elongation proceeds via an acyl-enzyme intermediate involving the second histidine in the canonical HxxHH motif. The unusual substrate-binding arrangement and chemistry suggest mechanisms for selective ELOVL inhibition, relevant for diseases where VLCFAs accumulate, such as X-linked adrenoleukodystrophy.
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http://dx.doi.org/10.1038/s41594-021-00605-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7611377PMC
June 2021

Structural Basis of Teneurin-Latrophilin Interaction in Repulsive Guidance of Migrating Neurons.

Cell 2020 01 9;180(2):323-339.e19. Epub 2020 Jan 9.

Department of Biochemistry, Oxford University, Oxford OX1 3QU, UK. Electronic address:

Teneurins are ancient metazoan cell adhesion receptors that control brain development and neuronal wiring in higher animals. The extracellular C terminus binds the adhesion GPCR Latrophilin, forming a trans-cellular complex with synaptogenic functions. However, Teneurins, Latrophilins, and FLRT proteins are also expressed during murine cortical cell migration at earlier developmental stages. Here, we present crystal structures of Teneurin-Latrophilin complexes that reveal how the lectin and olfactomedin domains of Latrophilin bind across a spiraling beta-barrel domain of Teneurin, the YD shell. We couple structure-based protein engineering to biophysical analysis, cell migration assays, and in utero electroporation experiments to probe the importance of the interaction in cortical neuron migration. We show that binding of Latrophilins to Teneurins and FLRTs directs the migration of neurons using a contact repulsion-dependent mechanism. The effect is observed with cell bodies and small neurites rather than their processes. The results exemplify how a structure-encoded synaptogenic protein complex is also used for repulsive cell guidance.
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http://dx.doi.org/10.1016/j.cell.2019.12.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6978801PMC
January 2020

The structural basis of lipid scrambling and inactivation in the endoplasmic reticulum scramblase TMEM16K.

Nat Commun 2019 09 2;10(1):3956. Epub 2019 Sep 2.

Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Old Road Campus Research Building, Roosevelt Drive, Oxford, OX3 7DQ, UK.

Membranes in cells have defined distributions of lipids in each leaflet, controlled by lipid scramblases and flip/floppases. However, for some intracellular membranes such as the endoplasmic reticulum (ER) the scramblases have not been identified. Members of the TMEM16 family have either lipid scramblase or chloride channel activity. Although TMEM16K is widely distributed and associated with the neurological disorder autosomal recessive spinocerebellar ataxia type 10 (SCAR10), its location in cells, function and structure are largely uncharacterised. Here we show that TMEM16K is an ER-resident lipid scramblase with a requirement for short chain lipids and calcium for robust activity. Crystal structures of TMEM16K show a scramblase fold, with an open lipid transporting groove. Additional cryo-EM structures reveal extensive conformational changes from the cytoplasmic to the ER side of the membrane, giving a state with a closed lipid permeation pathway. Molecular dynamics simulations showed that the open-groove conformation is necessary for scramblase activity.
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http://dx.doi.org/10.1038/s41467-019-11753-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6718402PMC
September 2019

Injectable cell-encapsulating composite alginate-collagen platform with inducible termination switch for safer ocular drug delivery.

Biomaterials 2019 05 5;201:53-67. Epub 2019 Feb 5.

Department of Ophthalmology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China. Electronic address:

Effective retinal drug delivery remains a challenge for treating vision-threatening diseases. Encapsulated-cell therapy (ECT) can provide local drug delivery without repeated invasive injections but is plagued by unsteady performance and biosafety issues. Here, an injectable composite alginate-collagen (CAC) ECT gel with a Tet-on inducible pro-caspase 8 mechanism that acted as an orally-inducible biosafety switch was developed for safer drug delivery. The optimised gels (2 mg/ml collagen, 1.5% high molecular weight alginate and 50,000 cells/gel) could be effectively terminated in vitro (≥20 pg/ml Doxycycline) and in vivo (1 mg/ml oral Doxycycline after 48 h). Also, they displayed effective proliferation control and continuous delivery of bioactive glial-cell derived neurotrophic factor (GDNF) with no significant gel degradation in vitro and in rat vitreous. Most importantly, intravitreally injected gels demonstrated therapeutic efficacy in Royal College of Surgeons rats with degenerating retina in reducing photoreceptor apoptosis and retina function loss. Furthermore, double gel injections into the same eye yielded better outcomes without compromising gel viability. Retrieved gels showed no host-tissue attachment or cell-protrusion 6 months post-implantation. The CAC ECT system exhibited mechanical stability, good encapsulation power, cell viability support, multiplexed GDNF dosage, and compatibility with different cell types (HEK293 and ARPE-19) without immunosuppressant, making it an attractive, safe and well-controlled platform for treating various eye diseases.
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http://dx.doi.org/10.1016/j.biomaterials.2019.01.032DOI Listing
May 2019

Structures of DPAGT1 Explain Glycosylation Disease Mechanisms and Advance TB Antibiotic Design.

Cell 2018 11;175(4):1045-1058.e16

Neurosciences Group, Nuffield Department of Clinical Neuroscience, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, OX3 9DS, UK.

Protein N-glycosylation is a widespread post-translational modification. The first committed step in this process is catalysed by dolichyl-phosphate N-acetylglucosamine-phosphotransferase DPAGT1 (GPT/E.C. 2.7.8.15). Missense DPAGT1 variants cause congenital myasthenic syndrome and disorders of glycosylation. In addition, naturally-occurring bactericidal nucleoside analogues such as tunicamycin are toxic to eukaryotes due to DPAGT1 inhibition, preventing their clinical use. Our structures of DPAGT1 with the substrate UDP-GlcNAc and tunicamycin reveal substrate binding modes, suggest a mechanism of catalysis, provide an understanding of how mutations modulate activity (thus causing disease) and allow design of non-toxic "lipid-altered" tunicamycins. The structure-tuned activity of these analogues against several bacterial targets allowed the design of potent antibiotics for Mycobacterium tuberculosis, enabling treatment in vitro, in cellulo and in vivo, providing a promising new class of antimicrobial drug.
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http://dx.doi.org/10.1016/j.cell.2018.10.037DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6218659PMC
November 2018

A new test strip technology platform for self-monitoring of blood glucose.

J Diabetes Sci Technol 2013 Sep 1;7(5):1386-99. Epub 2013 Sep 1.

Southwest Clinical Research Center, Santa Fe, New Mexico.

In the management of diabetes, accuracy of devices used for self-monitoring of blood glucose (SMBG) is critical because SMBG results can affect patient diabetes-related health outcomes. A new blood glucose monitoring system (BGMS) platform has been developed that is based on the new CONTOUR® NEXT (CN) test strip. This BGMS platform uses a proprietary electron mediator and algorithm to minimize errors at different steps in the testing process, thus minimizing outliers and significantly improving accuracy from prior-generation blood glucose meter systems. As demonstrated by questionnaire results from clinical studies with the new BGMS platform, accuracy and ease of use are important considerations for people with diabetes and their health care professionals when selecting an SMBG device. This article provides an overview of laboratory studies and clinical trials in the hands of lay users involving the performance of the portfolio of blood glucose meters that uses the new test strip. Each BGMS in the platform, which includes the CONTOUR XT (CONTOUR NEXT EZ in the United States), CONTOUR NEXT LINK, CONTOUR NEXT USB, and CN systems, demonstrated advanced accuracy both in the laboratory and in the hands of subjects (people with diabetes) and trained health care professionals. All systems met and exceeded International Organization for Standardization accuracy criteria (both ISO 15197:2003 and ISO 15197:2013). Each system in the new BGMS platform delivers advanced accuracy, which is essential to people who utilize SMBG for improved management.
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http://dx.doi.org/10.1177/193229681300700531DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3876385PMC
September 2013

A patient-centered approach to counseling patients with head and neck cancer undergoing human papillomavirus testing: a clinician's guide.

Oncologist 2013 23;18(2):180-9. Epub 2013 Jan 23.

Department of Otolaryngology, Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, Box 1189, New York, New York 10029, USA.

The International Agency for Research on Cancer and the National Cancer Institute have acknowledged human papillomavirus (HPV)-16 as an independent risk factor for oropharyngeal cancer (OPC). HPV-positive oropharyngeal cancer (HPVOPC) is a sexually transmitted entity that is on the rise; within the next 10 years, the annual number of HPV-associated OPC cases is projected to exceed the annual number of cervical cancer cases in the United States. Recognition of HPV status in OPC has broad implications beyond the traditional oncological concerns of timely diagnosis, accurate staging, and appropriate treatment of cancer patients. The National Comprehensive Cancer Network recommends testing the tumor site for HPV-status during OPC management; it is likely this will become a standard component of care for patients with high-probability tumors of the oropharynx. As the practice of HPV testing becomes more common, it behooves providers to be able to adequately address the concerns of patients with HPVOPC. Although there are currently few relevant studies focusing on this population, existing literature on HPV-infected women and patients with cervical cancer strongly supports the concept that patients with HPVOPC need education to optimally address concerns such as self-blame, guilt, intimacy, and interpersonal relationships. When HPV testing is done, it should be accompanied by evidence-driven and patient-centered counseling to best minimize negative psychosocial outcomes and ensure optimum health promotion. Based on the current state of the literature, this article is intended to be a reference for physicians to effectively manage psychosocial outcomes when diagnosing patients with HPV-associated OPC.
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http://dx.doi.org/10.1634/theoncologist.2012-0200DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3579602PMC
December 2013

Performance of a new blood glucose monitoring system in the hands of intended users.

Diabetes Technol Ther 2012 Sep 29;14(9):783-9. Epub 2012 Jun 29.

AMCR Institute Inc, Escondido, California 92026, USA.

Background: This study assessed the performance of a blood glucose monitoring system (BGMS) in development that uses a new generation of blood glucose test strips with capillary and venous blood in the hands of its intended users, people with diabetes and healthcare professionals (HCPs).

Subjects And Methods: In total, 93 subjects ≥ 18 years old (median age, 33 years) with type 1 (78%) or type 2 (22%) diabetes participated. Untrained subjects performed self-test fingersticks using a Microlet(®)2 lancing device (Bayer HealthCare LLC, Diabetes Care, Tarrytown, NY) followed by testing of their own capillary blood on the BGMS. HCPs performed fingersticks (using a Tenderlett(®) lancing device [International Technidyne Corp., Edison, NJ]) and venipunctures on subjects and tested both capillary and venous samples from subjects on the BGMS. All BGMS results were compared with Yellow Springs Instruments (YSI) (YSI Life Sciences, Inc., Yellow Springs, OH) laboratory results. Analytical accuracy was assessed according to International Organization for Standardization (ISO) 15197:2003 guidelines (i.e., within ± 15 mg/dL or ± 20% of the YSI results for samples with glucose concentrations < 75 mg/dL and ≥ 75 mg/dL, respectively) and more stringent criteria (i.e., within ± 15 mg/dL or ± 15% of the YSI results for samples with glucose concentrations < 100 mg/dL and ≥ 100 mg/dL, respectively).

Results: Overall, 98.9% (180/182) of subject Microlet2 capillary fingerstick results, 99.5% (182/183) of HCP Tenderlett capillary fingerstick results, and 100% (186/186) of venous results met current ISO criteria and more stringent criteria. The average hematocrit was 44%, with values ranging from 32% to 52%.

Conclusions: Test results from both capillary fingerstick and venous samples with a new BGMS in development met current accuracy guidelines as well as proposed tighter criteria.
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http://dx.doi.org/10.1089/dia.2012.0046DOI Listing
September 2012

Mapping the Queensland Health iPharmacy Medication File to the Australian Medicines Terminology Using Snapper.

Stud Health Technol Inform 2011 ;168:104-16

Clinical Information Management, Queensland Health, Brisbane, Australia.

An exploratory exercise in mapping approximately 8000 medication terms from the Queensland Health iPharmacy Medication File to the Australian Medicines Terminology (AMT) was carried out to determine coverage, build specialist knowledge, and inform future clinical terminology strategies. Snapper was the mapping tool selected for this exercise. The Automap function of the tool mapped 39.2% of the items that were successfully mapped, and the remainder were manually mapped. A total of 51.8% of the sample items were mapped to a semantically equivalent AMT concept with 50.0% of terms being mapped to a satisfactory fully specified term, and 1.8% of terms being mapped to a fully specified term that was considered unsuitable for QH clinical purposes. Rules and guidelines on how to deal with the emerging differences between the two terminologies were developed during the course of the project. Snapper was found to be an appropriate tool for this exercise; its functionality is being constantly refined to assist users. As a result, this exercise will provide NEHTA with input for the national scope and content for AMT, and QH will endeavour to prepare the iPharmacy medication file for future interfaces with other terminologies.
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January 2012

Cortical control of adaptive locomotion in wild-type mice and mutant mice lacking the ephrin-Eph effector protein alpha2-chimaerin.

J Neurophysiol 2010 Dec 29;104(6):3189-202. Epub 2010 Sep 29.

Department of Neuroscience, Columbia University, New York, New York, USA.

In voluntary control, supraspinal motor systems select the appropriate response and plan movement mechanics to match task constraints. Spinal circuits translate supraspinal drive into action. We studied the interplay between motor cortex (M1) and spinal circuits during voluntary movements in wild-type (WT) mice and mice lacking the α2-chimaerin gene (Chn1(-/-)), necessary for ephrinB3-EphA4 signaling. Chn1(-/-) mice have aberrant bilateral corticospinal systems, aberrant bilateral-projecting spinal interneurons, and disordered voluntary control because they express a hopping gait, which may be akin to mirror movements. We addressed three issues. First, we determined the role of the corticospinal system in adaptive control. We trained mice to step over obstacles during treadmill locomotion. We compared performance before and after bilateral M1 ablation. WT mice adaptively modified their trajectory to step over obstacles, and M1 ablation increased substantially the incidence of errant steps over the obstacle. Chn1(-/-) mice randomly stepped or hopped during unobstructed locomotion but hopped over the obstacle. Bilateral M1 ablation eliminated this obstacle-dependent hop selection and increased forelimb obstacle contact errors. Second, we characterized the laterality of corticospinal action in Chn1(-/-) mice using pseudorabies virus retrograde transneuronal transport and intracortical microstimulation. We showed bilateral connections between M1 and forelimb muscles in Chn1(-/-) and unilateral connections in WT mice. Third, in Chn1(-/-) mice, we studied adaptive responses before and after unilateral M1 ablation. We identified a more important role for contralateral than ipsilateral M1 in hopping over the obstacle. Our findings suggest an important role for M1 in the mouse in moment-to-moment adaptive control, and further, using Chn1(-/-) mice, a role in mediating task-dependent selection of mirror-like hopping movements over the obstacle. Our findings also stress the importance of subcortical control during adaptive locomotion because key features of the trajectory remained largely intact after M1 ablation.
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http://dx.doi.org/10.1152/jn.00671.2010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3007663PMC
December 2010

Intraocular impedance as a function of the position in the eye, electrode material and electrode size.

Conf Proc IEEE Eng Med Biol Soc 2004;2004:4169-71

Department of Electrical Engineering, University of Southern California, Los Angeles, CA, USA.

A critical element of a retinal prosthesis is the electrode assembly, which is placed on the retina. It is via this interface that the nerve cells are stimulated to produce the perception of light. The electrode impedance is an integral part in determining the design of the stimulating electrode and the attached circuit. The impedances involved are not only the tissue impedance but the electrode itself contributes to the impedance. Further on the electrode impedance depends not only the material of the electrode but also the size of the electrode. This paper discusses the results obtained by the intraocular impedance measurements with varying electrode size, electrode material and position of the electrode within the eye.
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http://dx.doi.org/10.1109/IEMBS.2004.1404163DOI Listing
September 2007

Stimulus induced pH changes in retinal implants.

Conf Proc IEEE Eng Med Biol Soc 2004;2004:4160-2

Second Sight Med. Products Inc., Sylmar, CA, USA.

Electrical stimulation of neural tissue requires charge injection into the biological environment. This is achieved through both Faradaic and non-Faradaic reactions at the electrode/tissue interface. Some Faradaic reactions have the potential to dramatically alter pH levels, leading to tissue damage. The present study looked to investigate the effects of stimulus induced pH changes for a variety of stimulation parameters in a retinal implant. Electrodes were stimulated using monophasic and biphasic pulses at different intensities and in different mediums. Stimulus frequency and pulse width were maintained consistent for all tests. pH levels were recorded using a pH microelectrode and verified using a pH color indicator (phenol red). As expected, no significant pH change could be detected in buffered saline or balanced salt solution. However, stimulation parameters causing pH changes could be detected in unbuffered saline solution. While electrode stimulation using biphasic charge-balanced current pulses showed minimal pH change, stimulation using monophasic pulses showed significant pH shifts. The extent of pH change was related to duration of stimulation. The results from this study provide an insight to the electrochemical mechanisms at the interface of the electrolyte medium and retinal stimulation electrodes.
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http://dx.doi.org/10.1109/IEMBS.2004.1404160DOI Listing
September 2007
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