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Characterization of (Boc‐Cys/Sec‐NHMe) 2 and (Boc‐Cys/Sec‐OMe) 2 : Evidence of local conformational difference between disulfide and diselenide
Author(s) -
Dolle Ashwini,
Reddy K. Kasi Amarnath,
Gunaga Shubha Shridhar,
Krishnamurthy Kiran,
Senapati Dillip Kumar,
Rana Abhijit,
Sindogi Kishorkumar,
Biswal Himansu S.,
Raghothama Srinivasarao,
Gowd Konkallu Hanumae
Publication year - 2020
Publication title -
journal of peptide science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 66
eISSN - 1099-1387
pISSN - 1075-2617
DOI - 10.1002/psc.3245
Subject(s) - diselenide , chemistry , antiparallel (mathematics) , crystallography , circular dichroism , stereochemistry , proton nmr , nuclear magnetic resonance spectroscopy , tripeptide , peptide , organic chemistry , selenium , biochemistry , physics , quantum mechanics , magnetic field
Conformations of disulfide and diselenide were compared in (Boc‐Cys/Sec‐NHMe) 2 and (Boc‐Cys/Sec‐OMe) 2 using X‐ray crystallography, nuclear magnetic resonance (NMR) spectroscopy, density functional theory (DFT), and circular dichroism (CD) spectroscopy. Conformations of disulfide/diselenide in polypeptides are defined based on the sign of side chain torsion angle χ 3 (–CH 2 –S/Se–S/Se–CH 2 –); negative indicates left‐handed and positive indicates right‐handed orientation. In the crystals of (Boc‐Cys‐OMe) 2 and (Boc‐Sec‐OMe) 2 , the disulfide exhibits a left‐handed and the diselenide a right‐handed orientation. Characterization of cystine and selenocystine derivatives in solution using 1 H‐NMR, natural abundant 77 Se NMR, 2D‐ROESY, and chemical shift analysis coupled to DMSO titration has indicated the symmetrical nature and antiparallel orientation of Cys/Sec residues about the disulfide/diselenide bridges. Structural calculations of cystine and selenocystine derivatives using DFT further support the antiparallel orientation of Cys/Sec residues about disulfide/diselenide. The far‐ultraviolet (UV) region CD spectra of cystine and selenocystine derivatives have exhibited the negative Cotton effect (CE) for disulfide and positive for diselenide confirming the difference in the conformational preference of disulfide and diselenide. In the previously reported polymorphic structure of (Boc‐Sec‐OMe) 2 , the diselenide has right‐handed orientation. In the X‐ray structures of disulfide and diselenide analogues of E scherichia coli protein encoded by curli specific gene C (CgsC) retrieved from Protein Databank (PDB), disulfide has left‐handed and the diselenide right‐handed orientation. The current report provides the evidence for the local conformational difference between a disulfide and a diselenide group under unconstrained conditions, which may be useful for the rational replacement of disulfide by diselenide in polypeptide chains.