The interaction of human serum albumin and model membranes

It is frequently observed that the interaction of human serum albumin (HSA) with different lipid membranes may affect molecular transport both in vivo and in vitro experiments. There was a lack of consensus however in the interpretation of results. Earlier studies on the serum albumin membrane association had different conclusions depending on the source of protein, the preparation and the composition of the membranes applied. In this work the change of heat capacity, a sensitive parameter of the interacting system, is compared for uni- and multilamellar liposomes (dimyristoyl-phosphatidylcoline/dimyristoyl-phosphatidylglycerol) at 0, 1x10(-3), 8x10(-3), 1.2x10(-2) and 3.3x10(-2) HSA-lipid ratios. The thermal properties of the sonicated and vortexed liposomes show remarkable differences. The presence of HSA in both types of liposomes also modified their thermal properties, providing clear evidence for protein-vesicle interaction, different in the uni- and multilamellar liposomes. In the case of unilamellar liposomes, two additional transitions were observed at lower temperature, independently of the HSA-lipid ratio, and the protein binding mode to smaller or larger sized liposomes was also distinguishable. The addition of HSA to the multilamellar liposomes resulted in an increase of the pretransition temperature only at the higher HSA-lipid ratio, but the main transition temperature was not affected.