* To whom correspondence should be addressed.
Received August 4, 2014; Revision received September 29, 2014
The immediate environment of the negatively charged membrane surface is characterized by decreased dielectric constant and pH value. These conditions can be modeled by water–alcohol mixtures at moderately low pH. Several globular proteins were investigated under these conditions, and their conformational behavior in the presence of phospholipid membranes was determined, as well as under conditions modeling the immediate environment of the membrane surface. These proteins underwent conformational transitions from the native to a molten globule-like state. Increased flexibility of the protein structure facilitated protein functioning. Our experimental data allow understanding forces that affect the structure of a protein functioning near the membrane surface (in other words, in the membrane field). Similar conformational states are widely reported in the literature. This indicates that the negatively charged membrane surface can serve as a moderately denaturing agent in the cell. We conclude that the effect of the membrane field on the protein structure must be taken into account.
KEY WORDS: anionic phospholipid membranes, simple alcohols as a model, globular proteins, apo- and holomyoglobins, apo- and holocytochromes c, cytochrome b5, human α-lactalbumin, conformational changes, non-native protein states, membrane–protein interactions pathways, membrane field