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Conformational analysis of a peptide approximating the HCCH motif in HIV‐1 Vif
Author(s) -
Giri Kalyan,
Maynard Ernest L.
Publication year - 2009
Publication title -
peptide science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.21209
Subject(s) - chemistry , zinc , peptide , cooperativity , cooperative binding , circular dichroism , apobec3g , tryptophan , binding site , stereochemistry , crystallography , protein structure , biophysics , biochemistry , amino acid , enzyme , biology , organic chemistry , cytidine deaminase
Virion infectivity factor (Vif) is an accessory protein encoded by HIV‐1. Vif recruits a Cul5‐based ubiquitin ligase that targets APOBEC3G, a host‐encoded antiviral enzyme, for proteasomal degradation. The C‐terminus of Vif contains a conserved His‐X 5 ‐Cys‐X 17‐18 ‐Cys‐X 3‐5 ‐His (HCCH) motif that binds zinc and interacts with Cul5. In this study, CD spectroscopy, fluorescence spectroscopy, light scattering, and zinc binding assays were used to examine the conformational properties of HCCHp, a 42‐amino acid peptide encompassing the HCCH motif. A single tryptophan residue was engineered into HCCHp to probe local structural changes induced by zinc binding. Zinc binding increased burial of the Trp residue from solvent and increased tertiary packing. The solvent 2,2,2‐trifluoroethanol (TFE) induced the formation of an α‐helical conformation of HCCHp with a midpoint of 20% (vol/vol) and inhibited zinc‐induced aggregation of HCCHp. TFE titration data were sigmoidal, consistent with the cooperative nature of helix formation. Zinc binding to HCCHp in 30% TFE solutions was cooperative and weakened the TFE‐induced structure. In 80% TFE solutions this cooperativity was lost, suggesting a mechanism in which monomeric and oligomeric peptide forms display different affinities for zinc. TFE weakened zinc binding to HCCHp by two orders of magnitude relative to the zinc binding affinity measured in aqueous solvent. The data suggest that HCCHp conformation and zinc binding affinity are tightly coupled. We propose that the lack of intrinsic structure in the HCCH motif may be important for Vif's function as an E3 ubiquitin ligase adaptor protein. © 2009 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 92: 417–425, 2009. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com