The protection of bovine serum albumin against thermal denaturation and gelation by sodium dodecyl sulfate studied by rheology and molecular dynamics simulation

摘要

It is well known that when bovine serum albumin (BSA) protein in aqueous solution is heated above the protein denaturation temperature which is typically > 65 degrees C, the protein unfolds substantially and under continuous heating the unfolded protein aggregates to form a gel. In contrast to conventional wisdom, however, we show that sodium dodecyl sulfate (SDS) can protect BSA against thermal denaturation and gelation at specific concentration range, using 0-1 M SDS and 3, 5 and 7 wt% BSA concentrations. The SDS protective effect which was investigated by time sweep test at 80 degrees C, increased with the SDS concentration up to 0.85, 0.7 and 0.4 M at 3, 5 and 7 wt% BSA solutions, respectively. Beyond these specified concentrations, the SDS protective effect decreased. The increase or decrease in the protective effect was further confirmed by the frequency sweep test carried out on the pure BSA and BSA/SDS solutions at 80 degrees C. The frequency sweep test showed that the value of the storage modulus (G') without the protective effect was more than 3 orders of magnitude larger than its value when the BSA was completely protected from thermal gelation. In order to interpret the SDS effects at the atomic/molecular level, molecular dynamics (MD) simulation was applied to identify the helices of the BSA that were protected in thermal denaturation at 80 degrees C. The molecular mechanism whereby SDS protects the BSA helices was established as a bridging interaction between the SDS ion and some helical moieties of the BSA.