Size of Unfolded and Dissociated Subunits versus that of Native Multimeric Proteins

Two factors, unfolding and dissociation, act in opposition indetermining the size of the unfolded state of multimeric proteins. Ananalysis has been presented to correlate relative expansion of the unfoldedmonomers in absence of disulfide bridges over the native state of differenthomomultimeric proteins of varying molecular weights. The Stoke's radii ofabout 70 proteins of Mw between 6 kDa to 4000 kDa and ranging frommonomers to dodecamers were calculated both under native anddenatured condition induced by 8 M urea or 6 M guanidinium,HClaccording to relations derived by Uversky [Biochemistry32 (1993), 13288-13298]. Stoke's radii of monomeric proteins were foundto increase by 1.6-2.2 times after denaturation as compared with the nativestate while that of the subunits of dimeric and tetrameric proteins wereincreased by factors 1.1-2.2 under the same conditions. For hexamericproteins this factor lies between 0.96-1.2. In each set the relativeincrement of the Stoke's radii followed a logarithmic relation with molecularweight and reached a minimum limiting value when Stoke's radii of nativeprotein became almost equal to that of the unfolded monomer.