Volumetric characterization of homopolymeric amino acids.
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 degrees C. In addition, we have determined at 25 degrees C changes in volume, DeltaV, and adiabatic compressibility, DeltaK(S), associated with the coil-to-helix transitions of poly(L-lysine) and poly(L-glutamic acid) and the alpha-to-beta 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 alpha-to-beta transition of poly(L-lysine) causes slight but statistically significant increases in volume and compressibility, an observation that may suggest that the beta-sheet conformation of poly(L-lysine) is slightly less hydrated than its alpha-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.
Noudeh
Gholamreza D
GD
Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, 19 Russell St., Toronto, Ontario M5S 2S2, Canada.
Taulier
Nicolas
N
Chalikian
Tigran V
TV
D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D010455:Peptides / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D011487:Protein Conformation; D013912:Threonine / Q000737:chemistry*
D010455:Peptides; D011108:Polymers; C011083:polyproline; C019529:polyalanine; D013912:Threonine