A systematic study of bovine serum albumin (BSA) and sodium dodecyl sulfate (SDS) interactions by surface tension and small angle X-ray scattering

摘要

Classical jpadrameters obtained from surface tension technique coupled to small anale X-ray scattering (SAXS) measurements gave support to investigate conformational changes in the bovine serum albumin (BSA)-sodium dodecyl sulfate (SDC) complexes as weell as the sixe of the micelle-like clusters distributed along the polypetide chain The studied systems were composed of 1 wt% of BSA in the absence and presence of increasing SDS molar concentration uo to 80 mM under experimental conditions of low ionic strength and pH 5.40 aT SDS concetrations below the critical aggregation concentration (cac) of 2.2 mM SAXS results indicte that the detefgent does not modify the native protein conformation.However the begining of protein unfolding evidenced by SAXS through an increase in the values of radius of gyration R_g and protein maxium dimension D_max is coincident with the onset of sds cooperative binding to BSA identified by the first breakpoint in the curface tesion-sds profile.Further SdS addition leads to the formation of micelle -like aggregates randomly distributed along the unfoled polypeptide chain consistent to a necklace and bead model The SAXS date also demonstrate that the SDS micelles grow in size up to 50 mM detergent At 50 mM surfactant the mixelles stop growing.This concentration is near the BSA satruation binding by sds measured by dialyzes and indicated by the second breakpoint in surface tension-sds profile.The SAXS and surface tension data are also consistent with teh formation of free micelles in equilibrium with BSA-SDS complexes for surfactant amount above the saturation.