The relationship between molecular weight and quaternary structure of globular proteins

The relationship between the molecular weight and the number of subunits in oligomeric globular proteins consisting of identical subunits has been analyzed. It has been shown that the molecular weights of the subunits are distributed about a mean value of 48,000 and consequently that the molecular weights of the native oligomeric proteins are distributed in clearly distinguishable molecular weight regions. This observation allows the probability of a particular oligomeric structure to be predicted from a measurement of the oligomer molecular weight alone, which is useful in a number of types of study of protein structure, particularly comparative studies. Calculations have been performed which suggest that there is no thermodynamic limitation, in terms of the subunit interactions themselves, to the size of an oligomeric protein with a given number of subunits. Rather, an individual polypeptide chain itself has inherent size limitations, which consequently limits the molecular weight of the corresponding oligomer.