Publications by authors named "Kun Hwa Lee"

3 Publications

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Molecular characterization of Hsf1 as a master regulator of heat shock response in the thermotolerant methylotrophic yeast Ogataea parapolymorpha.

J Microbiol 2021 Feb 1;59(2):151-163. Epub 2021 Feb 1.

Department of Life Science, College of Natural Science, Chung-Ang University, Seoul, 06974, Republic of Korea.

Ogataea parapolymorpha (Hansenula polymorpha DL-1) is a thermotolerant methylotrophic yeast with biotechnological applications. Here, O. parapolymorpha genes whose expression is induced in response to heat shock were identified by transcriptome analysis and shown to possess heat shock elements (HSEs) in their promoters. The function of O. parapolymorpha HSF1 encoding a putative heat shock transcription factor 1 (OpHsf1) was characterized in the context of heat stress response. Despite exhibiting low sequence identity (26%) to its Saccharomyces cerevisiae homolog, OpHsf1 harbors conserved domains including a DNA binding domain (DBD), domains involved in trimerization (TRI), transcriptional activation (AR1, AR2), transcriptional repression (CE2), and a C-terminal modulator (CTM) domain. OpHSF1 could complement the temperature sensitive (Ts) phenotype of a S. cerevisiae hsf1 mutant. An O. parapolymorpha strain with an H221R mutation in the DBD domain of OpHsf1 exhibited significantly retarded growth and a Ts phenotype. Intriguingly, the expression of heat-shock-protein-coding genes harboring HSEs was significantly decreased in the H221R mutant strain, even under non-stress conditions, indicating the importance of the DBD for the basal growth of O. parapolymorpha. Notably, even though the deletion of C-terminal domains (ΔCE2, ΔAR2, ΔCTM) of OpHsf1 destroyed complementation of the growth defect of the S. cerevisiae hsf1 strain, the C-terminal domains were shown to be dispensable in O. parapolymorpha. Overexpression of OpHsf1 in S. cerevisiae increased resistance to transient heat shock, supporting the idea that OpHsf1 could be useful in the development of heat-shock-resistant yeast host strains.
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http://dx.doi.org/10.1007/s12275-021-0646-2DOI Listing
February 2021

De novo proteins from random sequences through in vitro evolution.

Curr Opin Struct Biol 2021 Jan 28;68:129-134. Epub 2021 Jan 28.

Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN, USA; BioTechnology Institute, University of Minnesota, St. Paul, MN, USA. Electronic address:

Natural proteins are the result of billions of years of evolution. The earliest predecessors of today's proteins are believed to have emerged from random polypeptides. While we have no means to determine how this process exactly happened, there is great interest in understanding how it reasonably could have happened. We are reviewing how researchers have utilized in vitro selection and molecular evolution methods to investigate plausible scenarios for the emergence of early functional proteins. The studies range from analyzing general properties and structural features of unevolved random polypeptides to isolating de novo proteins with specific functions from synthetic randomized sequence libraries or generating novel proteins by combining evolution with rational design. While the results are exciting, more work is needed to fully unravel the mechanisms that seeded protein-dominated biology.
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http://dx.doi.org/10.1016/j.sbi.2020.12.014DOI Listing
January 2021

Genetic Code Evolution Investigated through the Synthesis and Characterisation of Proteins from Reduced-Alphabet Libraries.

Chembiochem 2019 03 15;20(6):846-856. Epub 2019 Feb 15.

Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN, 55455, USA.

The universal genetic code of 20 amino acids is the product of evolution. It is believed that earlier versions of the code had fewer residues. Many theories for the order in which amino acids were integrated into the code have been proposed, considering factors ranging from prebiotic chemistry to codon capture. Several meta-analyses combined these theories to yield a feasible consensus chronology of the genetic code's evolution, but there is a dearth of experimental data to test the hypothesised order. We used combinatorial chemistry to synthesise libraries of random polypeptides that were based on different subsets of the 20 standard amino acids, thus representing different stages of a plausible history of the alphabet. Four libraries were comprised of the five, nine, and 16 most ancient amino acids, and all 20 extant residues for a direct side-by-side comparison. We characterised numerous variants from each library for their solubility and propensity to form secondary, tertiary or quaternary structures. Proteins from the two most ancient libraries were more likely to be soluble than those from the extant library. Several individual protein variants exhibited inducible protein folding and other traits typical of intrinsically disordered proteins. From these libraries, we can infer how primordial protein structure and function might have evolved with the genetic code.
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http://dx.doi.org/10.1002/cbic.201800668DOI Listing
March 2019