National Center for
1EQ1: NMR STRUCTURE OF AN EXCHANGEABLE APOLIPOPROTEIN-MANDUCA SEXTA APOLIPOPHORIN-III
Structural basis for the conformational adaptability of apolipophorin III, a helix-bundle exchangeable apolipoprotein
Proc. Natl. Acad. Sci. U. S. A. (2002) 99 p.1188-1193» All references (2)
The high-resolution NMR structure of apolipophorin III from the sphinx moth, Manduca sexta, has been determined in the lipid-free state. We show that lipid-free apolipophorin III adopts a unique helix-bundle topology that has several characteristic structural features. These include a marginally stable, up-and-down helix bundle that allows for concerted opening of the bundle about "hinged" loops upon lipid interaction and buried polar/ionizable residues and buried interhelical H-bonds located in the otherwise hydrophobic interior of the bundle that adjust protein stability and facilitate lipid-induced conformational opening. We suggest that these structural features modulate the conformational adaptability of the lipid-free helix bundle upon lipid binding and control return of the open conformation to the original lipid-free helix-bundle state. Taken together, these data provide a structural rationale for the ability of exchangeable apolipoproteins to reversibly interact with circulating lipoprotein particles.