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Schmaltz LF, Koag MC, Kou Y, Zhang L, Lee S. Genotoxic effects of the major alkylation damage N7-methylguanine and methyl formamidopyrimidine. Biochem J 2023; 480:573-585. [PMID: 37078496 PMCID: PMC11061863 DOI: 10.1042/bcj20220460] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 03/29/2023] [Accepted: 04/19/2023] [Indexed: 04/21/2023]
Abstract
Various alkylating agents are known to preferentially modify guanine in DNA, resulting in the formation of N7-alkylguanine (N7-alkylG) and the imidazole ring opened alkyl-formamidopyrimidine (alkyl-FapyG) lesions. Evaluating the mutagenic effects of N7-alkylG has been challenging due to the instability of the positively charged N7-alkylG. To address this issue, we developed a 2'-fluorine-mediated transition-state destabilization approach, which stabilizes N7-alkylG and prevents spontaneous depurination. We also developed a postsynthetic conversion of 2'-F-N7-alkylG DNA into 2'-F-alkyl-FapyG DNA. Using these methods, we incorporated site-specific N7-methylG and methyl-FapyG into pSP189 plasmid and determined their mutagenic properties in bacterial cells using the supF-based colony screening assay. The mutation frequency of N7-methylG was found to be less than 0.5%. Our crystal structure analysis revealed that N7-methylation did not significantly alter base pairing properties, as evidenced by a correct base pairing between 2'-F-N7-methylG and dCTP in Dpo4 polymerase catalytic site. In contrast, the mutation frequency of methyl-FapyG was 6.3%, highlighting the mutagenic nature of this secondary lesion. Interestingly, all mutations arising from methyl-FapyG in the 5'-GGT(methyl-FapyG)G-3' context were single nucleotide deletions at the 5'-G of the lesion. Overall, our results demonstrate that 2'-fluorination technology is a useful tool for studying the chemically labile N7-alkylG and alkyl-FapyG lesions.
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Affiliation(s)
- Lillian F Schmaltz
- From the Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, U.S.A
| | - Myong-Chul Koag
- From the Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, U.S.A
| | - Yi Kou
- From the Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, U.S.A
| | - Louis Zhang
- From the Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, U.S.A
| | - Seongmin Lee
- From the Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, U.S.A
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2
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Rozelle AL, Cheun Y, Vilas CK, Koag MC, Lee S. DNA interstrand cross-links induced by the major oxidative adenine lesion 7,8-dihydro-8-oxoadenine. Nat Commun 2021; 12:1897. [PMID: 33772030 PMCID: PMC7997976 DOI: 10.1038/s41467-021-22273-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Accepted: 02/11/2021] [Indexed: 12/21/2022] Open
Abstract
Oxidative damage to DNA generates 7,8-dihydro-8-oxoguanine (oxoG) and 7,8-dihydro-8-oxoadenine (oxoA) as two major lesions. Despite the comparable prevalence of these lesions, the biological effects of oxoA remain poorly characterized. Here we report the discovery of a class of DNA interstrand cross-links (ICLs) involving oxidized nucleobases. Under oxidative conditions, oxoA, but not oxoG, readily reacts with an opposite base to produce ICLs, highlighting a latent alkylating nature of oxoA. Reactive halogen species, one-electron oxidants, and the myeloperoxidase/H2O2/Cl− system induce oxoA ICLs, suggesting that oxoA-mediated cross-links may arise endogenously. Nucleobase analog studies suggest C2-oxoA is covalently linked to N2-guanine and N3-adenine for the oxoA-G and oxoA-A ICLs, respectively. The oxoA ICLs presumably form via the oxidative activation of oxoA followed by the nucleophilic attack by an opposite base. Our findings provide insights into oxoA-mediated mutagenesis and contribute towards investigations of oxidative stress-induced ICLs and oxoA-based latent alkylating agents. 7,8-dihydro-8-oxoguanine and 7,8-dihydro-8-oxoadenine (oxoA) are generated upon oxidative damage to DNA, but the biological effects of oxoA are not well known. Here, the authors report that only oxoA forms DNA interstrand crosslinks (ICLs) upon secondary oxidation and that these ICLs can be induced by reactive halogen species, one-electron oxidants and the myeloperoxidase/H2O2/Cl- system.
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Affiliation(s)
- Aaron L Rozelle
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA.,McKetta Department of Chemical Engineering, Cockrell School of Engineering, The University of Texas at Austin, Austin, TX, USA
| | - Young Cheun
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - Caroline K Vilas
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA.,Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, TX, USA
| | - Myong-Chul Koag
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - Seongmin Lee
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA.
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3
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Koag MC, Jung H, Lee S. Mutagenesis mechanism of the major oxidative adenine lesion 7,8-dihydro-8-oxoadenine. Nucleic Acids Res 2020; 48:5119-5134. [PMID: 32282906 PMCID: PMC7229865 DOI: 10.1093/nar/gkaa193] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2020] [Revised: 03/06/2020] [Accepted: 04/07/2020] [Indexed: 12/20/2022] Open
Abstract
Reactive oxygen species generate the genotoxic 8-oxoguanine (oxoG) and 8-oxoadenine (oxoA) as major oxidative lesions. The mutagenicity of oxoG is attributed to the lesion's ability to evade the geometric discrimination of DNA polymerases by adopting Hoogsteen base pairing with adenine in a Watson–Crick-like geometry. Compared with oxoG, the mutagenesis mechanism of oxoA, which preferentially induces A-to-C mutations, is poorly understood. In the absence of protein contacts, oxoA:G forms a wobble conformation, the formation of which is suppressed in the catalytic site of most DNA polymerases. Interestingly, human DNA polymerase η (polη) proficiently incorporates dGTP opposite oxoA, suggesting the nascent oxoA:dGTP overcomes the geometric discrimination of polη. To gain insights into oxoA-mediated mutagenesis, we determined crystal structures of polη bypassing oxoA. When paired with dGTP, oxoA adopted a syn-conformation and formed Hoogsteen pairing while in a wobble geometry, which was stabilized by Gln38-mediated minor groove contacts to oxoA:dGTP. Gln38Ala mutation reduced misinsertion efficiency ∼55-fold, indicating oxoA:dGTP misincorporation was promoted by minor groove interactions. Also, the efficiency of oxoA:dGTP insertion by the X-family polβ decreased ∼380-fold when Asn279-mediated minor groove contact to dGTP was abolished. Overall, these results suggest that, unlike oxoG, oxoA-mediated mutagenesis is greatly induced by minor groove interactions.
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Affiliation(s)
- Myong-Chul Koag
- The Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, USA
| | - Hunmin Jung
- The Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, USA
| | - Seongmin Lee
- The Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, USA
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Koag MC, Jung H, Kou Y, Lee S. Bypass of the Major Alkylative DNA Lesion by Human DNA Polymerase η. Molecules 2019; 24:molecules24213928. [PMID: 31683505 PMCID: PMC6864850 DOI: 10.3390/molecules24213928] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2019] [Revised: 10/28/2019] [Accepted: 10/29/2019] [Indexed: 01/13/2023] Open
Abstract
A wide range of endogenous and exogenous alkylating agents attack DNA to generate various alkylation adducts. N7-methyl-2-deoxyguanosine (Fm7dG) is the most abundant alkylative DNA lesion. If not repaired, Fm7dG can undergo spontaneous depurination, imidazole ring-opening, or bypass by translesion synthesis DNA polymerases. Human DNA polymerase η (polη) efficiently catalyzes across Fm7dG in vitro, but its structural basis is unknown. Herein, we report a crystal structure of polη in complex with templating Fm7dG and an incoming nonhydrolyzable dCTP analog, where a 2'-fluorine-mediated transition destabilization approach was used to prevent the spontaneous depurination of Fm7dG. The structure showed that polη readily accommodated the Fm7dG:dCTP base pair with little conformational change of protein and DNA. In the catalytic site, Fm7dG and dCTP formed three hydrogen bonds with a Watson-Crick geometry, indicating that the major keto tautomer of Fm7dG is involved in base pairing. The polη-Fm7dG:dCTP structure was essentially identical to the corresponding undamaged structure, which explained the efficient bypass of the major methylated lesion. Overall, the first structure of translesion synthesis DNA polymerase bypassing Fm7dG suggests that in the catalytic site of Y-family DNA polymerases, small N7-alkylguanine adducts may be well tolerated and form the canonical Watson-Crick base pair with dCTP through their keto tautomers.
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Affiliation(s)
- Myong-Chul Koag
- The Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, 2409 University Avenue, TX 78712, USA.
| | - Hunmin Jung
- The Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, 2409 University Avenue, TX 78712, USA.
| | - Yi Kou
- The Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, 2409 University Avenue, TX 78712, USA.
| | - Seongmin Lee
- The Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, 2409 University Avenue, TX 78712, USA.
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Kou Y, Koag MC, Lee S. Promutagenicity of 8-Chloroguanine, A Major Inflammation-Induced Halogenated DNA Lesion. Molecules 2019; 24:molecules24193507. [PMID: 31569643 PMCID: PMC6804246 DOI: 10.3390/molecules24193507] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Revised: 09/26/2019] [Accepted: 09/26/2019] [Indexed: 12/18/2022] Open
Abstract
Chronic inflammation is closely associated with cancer development. One possible mechanism for inflammation-induced carcinogenesis is DNA damage caused by reactive halogen species, such as hypochlorous acid, which is released by myeloperoxidase to kill pathogens. Hypochlorous acid can attack genomic DNA to produce 8-chloro-2′-deoxyguanosine (ClG) as a major lesion. It has been postulated that ClG promotes mutagenic replication using its syn conformer; yet, the structural basis for ClG-induced mutagenesis is unknown. We obtained crystal structures and kinetics data for nucleotide incorporation past a templating ClG using human DNA polymerase β (polβ) as a model enzyme for high-fidelity DNA polymerases. The structures showed that ClG formed base pairs with incoming dCTP and dGTP using its anti and syn conformers, respectively. Kinetic studies showed that polβ incorporated dGTP only 15-fold less efficiently than dCTP, suggesting that replication across ClG is promutagenic. Two hydrogen bonds between syn-ClG and anti-dGTP and a water-mediated hydrogen bond appeared to facilitate mutagenic replication opposite the major halogenated guanine lesion. These results suggest that ClG in DNA promotes G to C transversion mutations by forming Hoogsteen base pairing between syn-ClG and anti-G during DNA synthesis.
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Affiliation(s)
- Yi Kou
- The Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, 2409 University Avenue, Austin, TX 78712, USA.
| | - Myong-Chul Koag
- The Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, 2409 University Avenue, Austin, TX 78712, USA.
| | - Seongmin Lee
- The Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, 2409 University Avenue, Austin, TX 78712, USA.
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Koag MC, Jung H, Lee S. Mutagenic Replication of the Major Oxidative Adenine Lesion 7,8-Dihydro-8-oxoadenine by Human DNA Polymerases. J Am Chem Soc 2019; 141:4584-4596. [PMID: 30817143 DOI: 10.1021/jacs.8b08551] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Reactive oxygen species attack DNA to produce 7,8-dihyro-8-oxoguanine (oxoG) and 7,8-dihydro-8-oxoadenine (oxoA) as major lesions. The structural basis for the mutagenicity of oxoG, which induces G to T mutations, is well understood. However, the structural basis for the mutagenic potential of oxoA, which induces A to C mutations, remains poorly understood. To gain insight into oxoA-induced mutagenesis, we conducted kinetic studies of human DNA polymerases β and η replicating across oxoA and structural studies of polβ incorporating dTTP/dGTP opposite oxoA. While polη readily bypassed oxoA, it incorporated dGTP opposite oxoA with a catalytic specificity comparable to that of correct insertion, underscoring the promutagenic nature of the major oxidative adenine lesion. Polη and polβ incorporated dGTP opposite oxoA ∼170-fold and ∼100-fold more efficiently than that opposite dA, respectively, indicating that the 8-oxo moiety greatly facilitated error-prone replication. Crystal structures of polβ showed that, when paired with an incoming dTTP, the templating oxoA adopted an anti conformation and formed Watson-Crick base pair. When paired with dGTP, oxoA adopted a syn conformation and formed a Hoogsteen base pair with Watson-Crick-like geometry, highlighting the dual-coding potential of oxoA. The templating oxoA was stabilized by Lys280-mediated stacking and hydrogen bonds. Overall, these results provide insight into the mutagenic potential and dual-coding nature of the major oxidative adenine lesion.
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Affiliation(s)
- Myong-Chul Koag
- The Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy , The University of Texas at Austin , Austin , Texas 78712 , United States
| | - Hunmin Jung
- The Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy , The University of Texas at Austin , Austin , Texas 78712 , United States
| | - Seongmin Lee
- The Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy , The University of Texas at Austin , Austin , Texas 78712 , United States
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Abstract
A wide variety of endogenous and exogenous alkylating agents attack DNA to preferentially generate N7-alkylguanine (N7-alkylG) adducts. Studies of the effect of N7-alkylG lesions on biological processes have been difficult in part because of complications arising from the chemical lability of the positively charged N7-alkylG, which can readily produce secondary lesions. To assess the effect of bulky N7-alkylG on DNA replication, we prepared chemically stable N7-benzylguanine (N7bnG)-containing DNA and evaluated nucleotide incorporation opposite the lesion by human DNA polymerase β (polβ), a model enzyme for high-fidelity DNA polymerases. Kinetic studies showed that the N7-benzyl-G lesion greatly inhibited dCTP incorporation by polβ. The crystal structure of polβ incorporating dCTP opposite N7bnG showed a Watson-Crick N7bnG:dCTP structure. The polβ-N7bnG:dCTP structure showed an open protein conformation, a relatively disordered dCTP, and a lack of catalytic metal, which explained the inefficient nucleotide incorporation opposite N7bnG. This indicates that polβ is sensitive to major groove adducts in the templating base side and deters nucleotide incorporation opposite bulky N7-alkylG adducts by adopting a catalytically incompetent conformation. Substituting Mg2+ for Mn2+ induced an open-to-closed conformational change due to the presence of catalytic metal and stably bound dCTP and increased the catalytic efficiency by ∼10-fold, highlighting the effect of binding of the incoming nucleotide and catalytic metal on protein conformation and nucleotidyl transfer reaction. Overall, these results suggest that, although bulky alkyl groups at guanine-N7 may not alter base pairing properties of guanine, the major groove-positioned lesions in the template could impede nucleotidyl transfer by some DNA polymerases.
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Affiliation(s)
- Yi Kou
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy , The University of Texas at Austin , Austin , Texas 78712 , United States
| | - Myong-Chul Koag
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy , The University of Texas at Austin , Austin , Texas 78712 , United States
| | - Seongmin Lee
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy , The University of Texas at Austin , Austin , Texas 78712 , United States
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Cheun Y, Koag MC, Naguib YW, Ouzon-Shubeita H, Cui Z, Pakotiprapha D, Lee S. Synthesis, structure, and biological evaluation of a platinum-carbazole conjugate. Chem Biol Drug Des 2017. [PMID: 28649747 DOI: 10.1111/cbdd.13062] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Cisplatin resistance is caused, in part, by the efficient removal of the helix-distorting cisplatin 1,2-intrastrand cross-links by nucleotide excision repair (NER) machinery. To make a platinum-DNA adduct that causes less helical distortion than the cisplatin 1,2-intrastrand adduct, we designed and synthesized a monofunctional platinum-carbazole conjugate (carbazoplatin). The 2.5 Å crystal structure of carbazoplatin-DNA adduct revealed both the monoplatination of the N7 of a guanine (G) base and the intercalation into two G:C base pairs, while causing a minor distortion of the DNA helix. A 50-mer dsDNA containing a single carbazoplatin lesion was poorly processed by UvrABC endonuclease, the prokaryotic NER machinery that detects helical distortion and performs dual incision around the lesion. Our cell viability assay indicated that the cytotoxic pathways of carbazoplatin might be different from those of cisplatin; carbazoplatin was 5-8 times more cytotoxic than cisplatin against PANC-1 and MDA-MB-231 cancer cell lines.
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Affiliation(s)
- Young Cheun
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - Myong-Chul Koag
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - Youssef W Naguib
- Division of Pharmaceutics, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA.,Department of Pharmaceutics, Faculty of Pharmacy, Minia University, Minia, Egypt
| | - Hala Ouzon-Shubeita
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - Zhengrong Cui
- Division of Pharmaceutics, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - Danaya Pakotiprapha
- Department of Biochemistry and Center of Excellence in Protein and Enzyme Technology, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Seongmin Lee
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
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Abstract
N7-Alkyl-2'-deoxyguanosines are major adducts in DNA that are generated by various alkylating mutagens and drugs. However, the effect of the N7 alkylation on the hydrogen-bonding patterns of the guanine remains poorly understood. We prepared N7-methyl-2'-deoxyguanosine (N7mdG)-containing DNA using a transition-state destabilization strategy, developed a novel polβ-host-guest complex system, and determined eight crystal structures of N7mdG or dG paired with dC, dT, dG, and dA. The structures of N7mdG:dC and N7mdG:dG are very similar to those of dG:dC and dG:dG, respectively, indicating the involvement of the keto tautomeric form of N7mdG in the base pairings with dC and dG. On the other hand, the structure of N7mdG:dT shows that the mispair forms three hydrogen bonds and adopts a Watson-Crick-like geometry rather than a wobble geometry, suggesting that the enol tautomeric form of N7mdG involves in its base pairing with dT. In addition, N7mdG:dA adopts a novel shifted anti:syn base pair presumably via the enol tautomeric form of N7mdG. The polβ-host-guest complex structures reveal that guanine-N7 methylation changes the hydrogen-bonding patterns of the guanine when paired with dT or dA and suggest that N7 alkylation may alter the base pairing patterns of guanine by promoting the formation of the rare enol tautomeric form of guanine.
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Affiliation(s)
- Yi Kou
- Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin , Austin, Texas 78712, United States
| | - Myong-Chul Koag
- Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin , Austin, Texas 78712, United States
| | - Seongmin Lee
- Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin , Austin, Texas 78712, United States
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Koag MC, Lai L, Lee S. Structural basis for the inefficient nucleotide incorporation opposite cisplatin-DNA lesion by human DNA polymerase β. J Biol Chem 2014; 289:31341-8. [PMID: 25237188 DOI: 10.1074/jbc.m114.605451] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Human DNA polymerase β (polβ) has been suggested to play a role in cisplatin resistance, especially in polβ-overexpressing cancer cells. Polβ has been shown to accurately albeit slowly bypass the cisplatin-1,2-d(GpG) (Pt-GG) intramolecular cross-link in vitro. Currently, the structural basis for the inefficient Pt-GG bypass mechanism of polβ is unknown. To gain structural insights into the mechanism, we determined two ternary structures of polβ incorporating dCTP opposite the templating Pt-GG lesion in the presence of the active site Mg(2+) or Mn(2+). The Mg(2+)-bound structure shows that the bulky Pt-GG adduct is accommodated in the polβ active site without any steric hindrance. In addition, both guanines of the Pt-GG lesion form Watson-Crick base pairing with the primer terminus dC and the incoming dCTP, providing the structural basis for the accurate bypass of the Pt-GG adduct by polβ. The Mn(2+)-bound structure shows that polβ adopts a catalytically suboptimal semiclosed conformation during the insertion of dCTP opposite the templating Pt-GG, explaining the inefficient replication across the Pt-GG lesion by polβ. Overall, our studies provide the first structural insights into the mechanism of the potential polβ-mediated cisplatin resistance.
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Affiliation(s)
- Myong-Chul Koag
- From the Division of Medicinal Chemistry, College of Pharmacy, The University of Texas, Austin, Texas 78712
| | - Lara Lai
- From the Division of Medicinal Chemistry, College of Pharmacy, The University of Texas, Austin, Texas 78712
| | - Seongmin Lee
- From the Division of Medicinal Chemistry, College of Pharmacy, The University of Texas, Austin, Texas 78712
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Abstract
To provide molecular-level insights into the spontaneous replication error and the mismatch discrimination mechanisms of human DNA polymerase β (polβ), we report four crystal structures of polβ complexed with dG•dTTP and dA•dCTP mismatches in the presence of Mg2+ or Mn2+. The Mg(2+)-bound ground-state structures show that the dA•dCTP-Mg2+ complex adopts an 'intermediate' protein conformation while the dG•dTTP-Mg2+ complex adopts an open protein conformation. The Mn(2+)-bound 'pre-chemistry-state' structures show that the dA•dCTP-Mn2+ complex is structurally very similar to the dA•dCTP-Mg2+ complex, whereas the dG•dTTP-Mn2+ complex undergoes a large-scale conformational change to adopt a Watson-Crick-like dG•dTTP base pair and a closed protein conformation. These structural differences, together with our molecular dynamics simulation studies, suggest that polβ increases replication fidelity via a two-stage mismatch discrimination mechanism, where one is in the ground state and the other in the closed conformation state. In the closed conformation state, polβ appears to allow only a Watson-Crick-like conformation for purine•pyrimidine base pairs, thereby discriminating the mismatched base pairs based on their ability to form the Watson-Crick-like conformation. Overall, the present studies provide new insights into the spontaneous replication error and the replication fidelity mechanisms of polβ.
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Affiliation(s)
- Myong-Chul Koag
- Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, USA
| | - Kwangho Nam
- Department of Chemistry and Computational Life Science Cluster (CLiC), Umeå University, 901 87 Umeå, Sweden
| | - Seongmin Lee
- Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, USA
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Koag MC, Kou Y, Ouzon-Shubeita H, Lee S. Transition-state destabilization reveals how human DNA polymerase β proceeds across the chemically unstable lesion N7-methylguanine. Nucleic Acids Res 2014; 42:8755-66. [PMID: 24966350 PMCID: PMC4117778 DOI: 10.1093/nar/gku554] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
N7-Methyl-2′-deoxyguanosine (m7dG) is the predominant lesion formed by methylating agents. A systematic investigation on the effect of m7dG on DNA replication has been difficult due to the chemical instability of m7dG. To gain insights into the m7dG effect, we employed a 2′-fluorine-mediated transition-state destabilzation strategy. Specifically, we determined kinetic parameters for dCTP insertion opposite a chemically stable m7dG analogue, 2′-fluoro-m7dG (Fm7dG), by human DNA polymerase β (polβ) and solved three X-ray structures of polβ in complex with the templating Fm7dG paired with incoming dCTP or dTTP analogues. The kinetic studies reveal that the templating Fm7dG slows polβ catalysis ∼300-fold, suggesting that m7dG in genomic DNA may impede replication by some DNA polymerases. The structural analysis reveals that Fm7dG forms a canonical Watson–Crick base pair with dCTP, but metal ion coordination is suboptimal for catalysis in the polβ-Fm7dG:dCTP complex, which partially explains the slow insertion of dCTP opposite Fm7dG by polβ. In addition, the polβ-Fm7dG:dTTP structure shows open protein conformations and staggered base pair conformations, indicating that N7-methylation of dG does not promote a promutagenic replication. Overall, the first systematic studies on the effect of m7dG on DNA replication reveal that polβ catalysis across m7dG is slow, yet highly accurate.
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Affiliation(s)
- Myong-Chul Koag
- Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, USA
| | - Yi Kou
- Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, USA
| | - Hala Ouzon-Shubeita
- Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, USA
| | - Seongmin Lee
- Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, USA
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Koag MC, Lee S. Metal-dependent conformational activation explains highly promutagenic replication across O6-methylguanine by human DNA polymerase β. J Am Chem Soc 2014; 136:5709-21. [PMID: 24694247 PMCID: PMC4004240 DOI: 10.1021/ja500172d] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
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Human
DNA polymerase β (polβ) inserts, albeit slowly,
T opposite the carcinogenic lesion O6-methylguanine (O6MeG) ∼30-fold
more frequently than C. To gain insight into this promutagenic process,
we solved four ternary structures of polβ with an incoming dCTP
or dTTP analogue base-paired with O6MeG in the presence of active-site
Mg2+ or Mn2+. The Mg2+-bound structures
show that both the O6MeG·dCTP/dTTP–Mg2+ complexes
adopt an open protein conformation, staggered base pair, and one active-site
metal ion. The Mn2+-bound structures reveal that, whereas
the O6Me·dCTP–Mn2+ complex assumes the similar
altered conformation, the O6MeG·dTTP–Mn2+ complex
adopts a catalytically competent state with a closed protein conformation
and pseudo-Watson–Crick base pair. On the basis of these observations,
we conclude that polβ slows nucleotide incorporation opposite
O6MeG by inducing an altered conformation suboptimal for catalysis
and promotes mutagenic replication by allowing Watson–Crick-mode
for O6MeG·T but not for O6MeG·C in the enzyme active site.
The O6MeG·dTTP–Mn2+ ternary structure, which
represents the first structure of mismatched polβ ternary complex
with a closed protein conformation and coplanar base pair, the first
structure of pseudo-Watson–Crick O6MeG·T formed in the
active site of a DNA polymerase, and a rare, if not the first, example
of metal-dependent conformational activation of a DNA polymerase,
indicate that catalytic metal-ion coordination is utilized as a kinetic
checkpoint by polβ and is crucial for the conformational activation
of polβ. Overall, our structural studies not only explain the
promutagenic polβ catalysis across O6MeG but also provide new
insights into the replication fidelity of polβ.
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Affiliation(s)
- Myong-Chul Koag
- Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin , Austin, Texas 78712, United States
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14
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Abstract
8-Halogenated guanine (haloG), a major DNA adduct formed by reactive halogen species during inflammation, is a promutagenic lesion that promotes misincorporation of G opposite the lesion by various DNA polymerases. Currently, the structural basis for such misincorporation is unknown. To gain insights into the mechanism of misincorporation across haloG by polymerase, we determined seven x-ray structures of human DNA polymerase β (polβ) bound to DNA bearing 8-bromoguanine (BrG). We determined two pre-catalytic ternary complex structures of polβ with an incoming nonhydrolyzable dGTP or dCTP analog paired with templating BrG. We also determined five binary complex structures of polβ in complex with DNA containing BrG·C/T at post-insertion and post-extension sites. In the BrG·dGTP ternary structure, BrG adopts syn conformation and forms Hoogsteen base pairing with the incoming dGTP analog. In the BrG·dCTP ternary structure, BrG adopts anti conformation and forms Watson-Crick base pairing with the incoming dCTP analog. In addition, our polβ binary post-extension structures show Hoogsteen BrG·G base pair and Watson-Crick BrG·C base pair. Taken together, the first structures of haloG-containing DNA bound to a protein indicate that both BrG·G and BrG·C base pairs are accommodated in the active site of polβ. Our structures suggest that Hoogsteen-type base pairing between G and C8-modified G could be accommodated in the active site of a DNA polymerase, promoting G to C mutation.
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Affiliation(s)
- Myong-Chul Koag
- From the Division of Medicinal Chemistry, College of Pharmacy, the University of Texas, Austin, Texas 78712
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Tsirulnikov K, Abuladze N, Koag MC, Newman D, Scholz K, Bondar G, Zhu Q, Avliyakulov NK, Dekant W, Faull K, Kurtz I, Pushkin A. Transport of N-acetyl-S-(1,2-dichlorovinyl)-L-cysteine, a metabolite of trichloroethylene, by mouse multidrug resistance associated protein 2 (Mrp2). Toxicol Appl Pharmacol 2010; 244:218-25. [PMID: 20060011 DOI: 10.1016/j.taap.2009.12.035] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2009] [Revised: 12/18/2009] [Accepted: 12/22/2009] [Indexed: 12/20/2022]
Abstract
N-acetyl-S-(1,2-dichlorovinyl)-l-cysteine (Ac-DCVC) and S-(1,2-dichlorovinyl)-l-cysteine (DCVC) are the glutathione conjugation pathway metabolites of a common industrial contaminant and potent nephrotoxicant trichloroethylene (TCE). Ac-DCVC and DCVC are accumulated in the renal proximal tubule where they may be secreted into the urine by an unknown apical transporter(s). In this study, we explored the hypothesis that the apical transport of Ac-DCVC and/or DCVC may be mediated by the multidrug resistance associated protein 2 (Mrp2, ABCC2), which is known to mediate proximal tubular apical ATP-dependent transport of glutathione and numerous xenobiotics and endogenous substances conjugated with glutathione. Transport experiments using membrane vesicles prepared from mouse proximal tubule derived cells expressing mouse Mrp2 utilizing ATPase assay and direct measurements of Ac-DCVC/DCVC using liquid chromatography/tandem mass-spectrometry (LC/MS/MS) demonstrated that mouse Mrp2 mediates ATP-dependent transport of Ac-DCVC. Expression of mouse Mrp2 antisense mRNA significantly inhibited the vectorial basolateral to apical transport of Ac-DCVC but not DCVC in mouse proximal tubule derived cells endogenously expressing mouse Mrp2. The results suggest that Mrp2 may be involved in the renal secretion of Ac-DCVC.
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Affiliation(s)
- Kirill Tsirulnikov
- Department of Medicine/Nephrology, David Geffen School of Medicine, University of California at Los Angeles, CA 90095, USA
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16
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Abstract
The nature and magnitude of voltage sensor conformational changes during ion channel activation are controversial. We have analyzed the topology of the K(V)AP voltage sensor domain in the absence and presence of a hyperpolarized voltage using native, right-side out membrane vesicles from E. coli. This approach does not disrupt the normal membrane environment of the channel protein and does not involve detergent solubilization. We found that voltage-dependent conformational changes are focused in the N-terminal half of the K(V)AP S4 segment, in excellent agreement with results obtained with Shaker. Homologous residues in the K(V)AP and Shaker S4 segments are transferred from the extracellular to the intracellular compartment upon hyperpolarization. Taken together with X-ray structures indicating that the K(V)AP S4 segment is outwardly displaced at 0 mV compared to S4 in a mammalian Shaker channel, our results are consistent with the idea that S4 moves further during voltage-dependent activation in K(V)AP than in Shaker.
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Affiliation(s)
- Myong-Chul Koag
- Department of Physiology and Molecular Biology Institute, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, USA
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Koag MC, Wilkens S, Fenton RD, Resnik J, Vo E, Close TJ. The K-segment of maize DHN1 mediates binding to anionic phospholipid vesicles and concomitant structural changes. Plant Physiol 2009; 150:1503-14. [PMID: 19439573 PMCID: PMC2705017 DOI: 10.1104/pp.109.136697] [Citation(s) in RCA: 151] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2009] [Accepted: 05/06/2009] [Indexed: 05/18/2023]
Abstract
Dehydrins (DHNs; late embryogenesis abundant D11 family) are a family of intrinsically unstructured plant proteins that accumulate in the late stages of seed development and in vegetative tissues subjected to water deficit, salinity, low temperature, or abscisic acid treatment. We demonstrated previously that maize (Zea mays) DHNs bind preferentially to anionic phospholipid vesicles; this binding is accompanied by an increase in alpha-helicity of the protein, and adoption of alpha-helicity can be induced by sodium dodecyl sulfate. All DHNs contain at least one "K-segment," a lysine-rich 15-amino acid consensus sequence. The K-segment is predicted to form a class A2 amphipathic alpha-helix, a structural element known to interact with membranes and proteins. Here, three K-segment deletion proteins of maize DHN1 were produced. Lipid vesicle-binding assays revealed that the K-segment is required for binding to anionic phospholipid vesicles, and adoption of alpha-helicity of the K-segment accounts for most of the conformational change of DHNs upon binding to anionic phospholipid vesicles or sodium dodecyl sulfate. The adoption of structure may help stabilize cellular components, including membranes, under stress conditions.
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Affiliation(s)
- Myong-Chul Koag
- Graduate Program in Biochemistry and Molecular Biology, University of California, Riverside, California 92521-0124, USA
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Koag MC, Wilkens S, Fenton RD, Resnik J, Vo E, Close TJ. The K-segment of maize DHN1 mediates binding to anionic phospholipid vesicles and concomitant structural changes. Plant Physiol 2009. [PMID: 19439573 DOI: 10.1104/pp109136697] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Dehydrins (DHNs; late embryogenesis abundant D11 family) are a family of intrinsically unstructured plant proteins that accumulate in the late stages of seed development and in vegetative tissues subjected to water deficit, salinity, low temperature, or abscisic acid treatment. We demonstrated previously that maize (Zea mays) DHNs bind preferentially to anionic phospholipid vesicles; this binding is accompanied by an increase in alpha-helicity of the protein, and adoption of alpha-helicity can be induced by sodium dodecyl sulfate. All DHNs contain at least one "K-segment," a lysine-rich 15-amino acid consensus sequence. The K-segment is predicted to form a class A2 amphipathic alpha-helix, a structural element known to interact with membranes and proteins. Here, three K-segment deletion proteins of maize DHN1 were produced. Lipid vesicle-binding assays revealed that the K-segment is required for binding to anionic phospholipid vesicles, and adoption of alpha-helicity of the K-segment accounts for most of the conformational change of DHNs upon binding to anionic phospholipid vesicles or sodium dodecyl sulfate. The adoption of structure may help stabilize cellular components, including membranes, under stress conditions.
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Affiliation(s)
- Myong-Chul Koag
- Graduate Program in Biochemistry and Molecular Biology, University of California, Riverside, California 92521-0124, USA
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Tsirulnikov K, Abuladze N, Newman D, Ryazantsev S, Wolak T, Magilnick N, Koag MC, Kurtz I, Pushkin A. Mouse aminoacylase 3: a metalloenzyme activated by cobalt and nickel. Biochim Biophys Acta 2009; 1794:1049-57. [PMID: 19362172 DOI: 10.1016/j.bbapap.2009.03.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2008] [Revised: 03/30/2009] [Accepted: 03/31/2009] [Indexed: 01/07/2023]
Abstract
Aminoacylase 3 (AA3) deacetylates N-acetyl-aromatic amino acids and mercapturic acids including N-acetyl-1,2-dichlorovinyl-L-cysteine (Ac-DCVC), a metabolite of a xenobiotic trichloroethylene. Previous studies did not demonstrate metal-dependence of AA3 despite a high homology with a Zn(2+)-metalloenzyme aminoacylase 2 (AA2). A 3D model of mouse AA3 was created based on homology with AA2. The model showed a putative metal binding site formed by His21, Glu24 and His116, and Arg63, Asp68, Asn70, Arg71, Glu177 and Tyr287 potentially involved in catalysis/substrate binding. The mutation of each of these residues to alanine inactivated AA3 except Asn70 and Arg71, therefore the corrected 3D model of mouse AA3 was created. Wild type (wt) mouse AA3 expressed in E. coli contained approximately 0.35 zinc atoms per monomer. Incubation with Co(2+) and Ni(2+) activated wt-AA3. In the cobalt-activated AA3 zinc was replaced with cobalt. Metal removal completely inactivated wt-AA3, whereas addition of Zn(2+), Mn(2+) or Fe(2+) restored initial activity. Co(2+) and to a lesser extent Ni(2+) increased activity several times in comparison with intact wt-AA3. Co(2+) drastically increased the rate of deacetylation of Ac-DCVC and significantly increased the toxicity of Ac-DCVC in the HEK293T cells expressing wt-AA3. The results indicate that AA3 is a metalloenzyme significantly activated by Co(2+) and Ni(2+).
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Affiliation(s)
- Kirill Tsirulnikov
- Department of Medicine, David Geffen School of Medicine, University of California at Los Angeles, CA 90095, USA
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Koag MC, Fenton RD, Wilkens S, Close TJ. The binding of maize DHN1 to lipid vesicles. Gain of structure and lipid specificity. Plant Physiol 2003; 131:309-16. [PMID: 12529538 PMCID: PMC166810 DOI: 10.1104/pp.011171] [Citation(s) in RCA: 198] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2002] [Revised: 09/06/2002] [Accepted: 10/08/2002] [Indexed: 05/18/2023]
Abstract
Dehydrins (DHNs; late embryogenesis abundant D-11) are a family of plant proteins induced in response to abiotic stresses such as drought, low temperature, and salinity or during the late stages of embryogenesis. Spectral and thermal properties of these proteins in purified form suggest that they are "intrinsically unstructured." However, DHNs contain at least one copy of a consensus 15-amino acid sequence, the "K segment," which resembles a class A2 amphipathic alpha-helical, lipid-binding domain found in other proteins such as apolipoproteins and alpha-synuclein. The presence of the K segment raises the question of whether DHNs bind lipids, bilayers, or phospholipid vesicles. Here, we show that maize (Zea mays) DHN DHN1 can bind to lipid vesicles that contain acidic phospholipids. We also observe that DHN1 binds more favorably to vesicles of smaller diameter than to larger vesicles, and that the association of DHN1 with vesicles results in an apparent increase of alpha-helicity of the protein. Therefore, DHNs, and presumably somewhat similar plant stress proteins in the late embryogenesis abundant and cold-regulated classes may undergo function-related conformational changes at the water/membrane interface, perhaps related to the stabilization of vesicles or other endomembrane structures under stress conditions.
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Affiliation(s)
- Myong-Chul Koag
- Graduate Program in Biochemistry and Molecular Biology, University of California, Riverside, California 92521-0124, USA
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