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Jayaraj A, Schwanz HA, Spencer DJ, Bhasin S, Hamilton JA, Jayaram B, Goldman AL, Krishna M, Krishnan M, Shah A, Jin Z, Krenzel E, Nair SN, Ramesh S, Guo W, Wagner G, Arthanari H, Peng L, Lawney B, Jasuja R. Allosterically Coupled Multisite Binding of Testosterone to Human Serum Albumin. Endocrinology 2021; 162:5944062. [PMID: 33125473 PMCID: PMC7774055 DOI: 10.1210/endocr/bqaa199] [Citation(s) in RCA: 9] [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] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Indexed: 12/25/2022]
Abstract
Human serum albumin (HSA) acts as a carrier for testosterone, other sex hormones, fatty acids, and drugs. However, the dynamics of testosterone's binding to HSA and the structure of its binding sites remain incompletely understood. Here, we characterize the dynamics of testosterone's binding to HSA and the stoichiometry and structural location of the binding sites using 2-dimensional nuclear magnetic resonance (2D NMR), fluorescence spectroscopy, 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid dipotassium salt partitioning, and equilibrium dialysis, complemented by molecular modeling. 2D NMR studies showed that testosterone competitively displaced 18-[13C]-oleic acid from at least 3 known fatty acid binding sites on HSA that also bind many drugs. Binding isotherms of testosterone's binding to HSA generated using fluorescence spectroscopy and equilibrium dialysis were nonlinear and the apparent dissociation constant varied with different concentrations of testosterone and HSA. The binding isotherms neither conformed to a linear binding model with 1:1 stoichiometry nor to 2 independent binding sites; the binding isotherms were most consistent with 2 or more allosterically coupled binding sites. Molecular dynamics studies revealed that testosterone's binding to fatty acid binding site 3 on HSA was associated with conformational changes at site 6, indicating that residues in in these 2 distinct binding sites are allosterically coupled. There are multiple, allosterically coupled binding sites for testosterone on HSA. Testosterone shares these binding sites on HSA with free fatty acids, which could displace testosterone from HSA under various physiological states or disease conditions, affecting its bioavailability.
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Affiliation(s)
- Abhilash Jayaraj
- Department of Chemistry, Bioinformatics and Computational Biology, Kusuma School of Biological Sciences, Indian Institute of Technology, New Delhi, India
| | - Heidi A Schwanz
- Department of Biophysics, Boston University School of Medicine, Boston, MA, USA
| | - Daniel J Spencer
- Research Program in Men’s Health: Aging and Metabolism, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
| | - Shalender Bhasin
- Research Program in Men’s Health: Aging and Metabolism, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
| | - James A Hamilton
- Department of Biophysics, Boston University School of Medicine, Boston, MA, USA
| | - B Jayaram
- Department of Chemistry, Bioinformatics and Computational Biology, Kusuma School of Biological Sciences, Indian Institute of Technology, New Delhi, India
| | - Anna L Goldman
- Research Program in Men’s Health: Aging and Metabolism, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
| | - Meenakshi Krishna
- Research Program in Men’s Health: Aging and Metabolism, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
| | - Maya Krishnan
- Research Program in Men’s Health: Aging and Metabolism, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
| | - Aashay Shah
- Division of Medicinal and Natural Products Chemistry, Department of Pharmaceutical Sciences and Experimental Therapeutics, College of Pharmacy, University of Iowa, Iowa City, IA, USA
| | - Zhendong Jin
- Division of Medicinal and Natural Products Chemistry, Department of Pharmaceutical Sciences and Experimental Therapeutics, College of Pharmacy, University of Iowa, Iowa City, IA, USA
| | - Eileen Krenzel
- Department of Biophysics, Boston University School of Medicine, Boston, MA, USA
| | - Sashi N Nair
- Research Program in Men’s Health: Aging and Metabolism, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
| | - Sid Ramesh
- Research Program in Men’s Health: Aging and Metabolism, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
| | - Wen Guo
- Research Program in Men’s Health: Aging and Metabolism, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
| | - Gerhard Wagner
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
| | - Haribabu Arthanari
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
| | - Liming Peng
- Research Program in Men’s Health: Aging and Metabolism, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
| | - Brian Lawney
- Department of Biostatistics, Harvard School of Public Health, Boston, MA, USA
| | - Ravi Jasuja
- Research Program in Men’s Health: Aging and Metabolism, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
- Correspondence: Ravi Jasuja, Research Program in Men’s Health: Aging and Metabolism, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02115. E-mail:
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Dolai S, Cherakara S, Garai K. Apolipoprotein E4 exhibits intermediates with domain interaction. Biochim Biophys Acta Proteins Proteom 2020; 1868:140535. [PMID: 32882410 DOI: 10.1016/j.bbapap.2020.140535] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Revised: 08/18/2020] [Accepted: 08/27/2020] [Indexed: 11/23/2022]
Abstract
ApoE4(C112R) is the strongest risk factor for Alzheimer's disease, while apoE3(C112) is considered normal. The C112R substitution is believed to alter the interactions between the N-terminal (NTD) and the C-terminal domain (CTD) leading to major functional differences. Here we investigate how the molecular property of the residue at position 112 affects domain interaction using an array of C112X substitutions with arginine, alanine, threonine, valine, leucine and isoleucine as 'X'. We attempt to determine the free energy of domain interaction (∆GINT) from stabilities of the NTD (∆GNTD) and CTD (∆GCTD) in the full-length apoE, and the stabilities of fragments of the NTD (∆GNTF) and CTD (∆GCTF), using the relationship, ∆GINT = ∆GNTD + ∆GCTD - ∆GNTF - ∆GCTF. We find that although ∆GNTD is strongly dependent on the C112X substitutions, ∆GNTD - ∆GNTF is small. Furthermore, ∆GCTD remains nearly the same as ∆GCTF. Therefore, ∆GINT is estimated to be small and similar for the apoE isoforms. However, stability of domain interaction monitored by urea dependent changes in interdomain Forster Resonance Energy Transfer (FRET) is found to be strongly dependent on C112X substitutions. ApoE4 exhibits the highest mid-point of denaturation of interdomain FRET. To resolve the apparently contradictory observations, we hypothesize that higher interdomain FRET in apoE4 in urea may involve 'intermediate' states. Enhanced fluorescence of bis-ANS and susceptibility to proteolytic cleavage support that apoE4, specifically, the NTD of apoE4 harbor 'intermediates' in both native and mildly denaturing conditions. The intermediates could hold key to the pathological functions of apoE4.
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