Effect of pH on the conformation of bovine serume albumin - gold bioconjugates

Biodegradable, biocompatible nanoparticles with tuneable fluorescence - due to their great potential in biology, medicine and sensor development - are widely studied nowadays. Recently it was shown that the complex red emitting spectroscopic feature of Bovine Serum Albumin - gold (BSAAu) bioconjugates can be related to the versatility of conformational changes of the BSA protein. In our study, we performed a comprehensive study on the structural changes of the host BSA molecules by infrared spectroscopy (FTIR) and small-angle X-ray scattering (SAXS). Both methods revealed that the BSA structure is not reversible after a neutral - alkali - neutral pH cycle and this behaviour is more pronounced in the presence of the gold salt (HAuCl4). The changes in the monitored secondary structural elements of BSA-(HAuCl4) system, with the fitted molecular shapes indicate that all steps in the synthesis route influence both the fine and the global structures of BSA and result in a complex structural prehistory dependent hindering of the total structural reversibility. A robust connection exists between the structural/conformational changes and the fluorescence behaviours.