Effects of disulfide bonds on compactness of protein molecules revealed by volume, compressibility, and expansibility changes during reduction.
To elucidate the effects of disulfide bonds on the compactness of protein molecules, the partial specific volume (v(o)) and coefficients of adiabatic compressibility (beta(s)(o)) and thermal expansibility (alpha) of five globular proteins (ovalbumin, beta-lactoglobulin, lysozyme, ribonuclease A, and bovine serum albumin) were measured in aqueous solutions with pH values of 7 and 2 at 25 degrees C when their disulfide bonds were totally reduced by carboxamidomethylation. Circular dichroism and fluorescence spectra show that the secondary and tertiary structures are partly disrupted by reduction, depending on the number of disulfide bonds in the proteins and the pH of the medium. The conformational changes are accompanied by decreases in v(o) and beta(s)(o) and by an increase in alpha, indicating that reduction decreases the internal cavity and increases surface hydration. The beta(s)(o) values of native or oxidized proteins decrease, and the effects of reduction on the volumetric parameters become more significant as the number of disulfide bonds increases and as they are formed over a larger distance in the primary structure. These results demonstrate that disulfide bonds play an important role, mainly via entropic forces, in the three-dimensional structure and compactness of protein molecules.
Gekko
Kunihiko
K
Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan. gekko@sci.hiroshima-u.ac.jp
Kimoto
Akinobu
A
Kamiyama
Tadashi
T
D000818:Animals; D002417:Cattle; D002645:Chickens; D002942:Circular Dichroism; D019245:Compressive Strength; D004220:Disulfides / Q000737:chemistry*; D004548:Elasticity; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013552:Swine; D013696:Temperature; D013816:Thermodynamics
D004220:Disulfides; D011506:Proteins