Mass-action driven conformational switching of proteins: investigation of beta-lactoglobulin dimerisation by infrared spectroscopy

Abstract

We study the dimerisation of beta-lactoglobulin (type A) at concentrations between 10 mg ml(-1) and 200 mg ml(-1) at fixed pH 3 and an ionic strength of 1.2 M and show that the degree of dimerisation can be determined from the coherent change in the ATR FTIR spectrum due to changes in folding induced by the dimerisation. This allows us to determine the IR spectrum of monomeric BLG and the dimerisation constant for which we find a value of K = 1.84 (+/- 0.5) . 10(2) M-1. Furthermore, we show that including self-crowding effects at high concentrations accounts for the concentration dependence of the apparent dimerisation constant.