Protein-lipid interactions of the human erythrocyte anion transporter, band 3
Abstract
The interactions between bilayer-forming lipids and the membrane-spanning domain of the human erythrocyte anion transporter, band 3, were investigated in order to obtain a better understanding of how bilayer lipids contribute to the stability of membrane spanning proteins. This was accomplished by reconstituting the purified, delipidated transporter into lipid vesicles of defined composition and examining the resulting proteoliposomes by highly sensitive differential scanning calorimetry. In addition, the fatty acid composition of the phospholipids which copurify with the integral domain was determined to test the hypothesis that the lipids which contribute the most stability to membrane spanning proteins are also those which bind most tightly to this important, yet poorly understood, class of proteins. The lipids were varied with respect to the head group type, the acyl chain length, the degree of unsaturation, and the amount of cholesterol. The results indicate that, in general, the lipids which contribute the greatest amount of stability to the membrane-spanning domain are those which create a thicker bilayer. Thus, zwitterionic lipids containing long, saturated acyl moieties resulted in bilayers in which band 3 was most stable. The addition of cholesterol, which also may thicken the bilayer, also increased the stability of the anion transporter. These results are especially meaningful because band 3 is thought to possess an unusually long membrane spanning region. Analysis of the fatty acid composition of the lipids which copurify with band 3 show that these lipids, which are assumed to be the most tightly bound class of phospholipids, contain acyl moieties which would strongly stabilize the protein. Thus any preferential interactions between integral membrane proteins and the bilayer lipids seem to be dictated, at least in part, by the complimentarity of their respective hydrophobic zones.
Degree
Ph.D.
Advisors
Low, Purdue University.
Subject Area
Biochemistry
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