Volumetric characterization of homopolymeric amino acids

✍ Scribed by Gholamreza D. Noudeh; Nicolas Taulier; Tigran V. Chalikian

• Publisher: Wiley (John Wiley & Sons)
• Year: 2003
• Tongue: English
• Weight: 151 KB
• Volume: 70
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.10526

✦ Synopsis

Abstract

We have determined the partial molar volumes, expansibilities, and adiabatic compressibilities for poly(L‐alanine), poly(L‐proline), and poly(L‐threonine) within the temperature range of 18–55°C. In addition, we have determined at 25°C changes in volume, Δ__V__, and adiabatic compressibility, Δ__K__~S~, associated with the coil‐to‐helix transitions of poly(L‐lysine) and poly(L‐glutamic acid) and the α‐to‐β transition of poly(L‐lysine). We have interpreted our volumetric data as suggesting that poly(L‐alanine) and poly(L‐proline) are not fully unfolded and, probably, retain some solvent‐inaccessible core. Further, we propose that poly(L‐threonine) is fully unfolded with the majority of its atomic groups being solvent‐exposed. Near zero changes in volume and compressibility accompanying the coil‐to‐helix transitions of poly(L‐lysine) and poly(L‐glutamic acid) suggest that, in the absence of fortuitous compensations, the coil‐to‐helix transitions of the polypeptides do not result in any significant enhancement of solute hydration. By contrast, the α‐to‐β transition of poly(L‐lysine) causes slight but statistically significant increases in volume and compressibility, an observation that may suggest that the β‐sheet conformation of poly(L‐lysine) is slightly less hydrated than its α‐helical conformation. In general, our results provide a quantitative volumetric description of the hydration properties of the homopolymeric polypeptides investigated. Such characterizations should prove useful in developing an understanding of the role that solvent plays in the stabilization/destabilization of folded protein structures and protein complexes. © 2003 Wiley Periodicals, Inc. Biopolymers 70: 563–574, 2003