Secondary structures of synthetic peptides corresponding to the first membrane-contact portion of normal band 3 and its deletion mutant (Southeast Asian ovalocytosis).

The conformations of synthetic peptides corresponding to the first membrane-contact portion from Tyr390 to Lys430 of band 3 (band 3-1a) and the counterpart portion of South-East Asian ovalocytosis (SAO) band 3 (band 3-1b) in lipid bilayers were examined by means of circular dichroism (CD), Fourier transform infrared (FTIR) spectroscopy as well as a proteolytic digestion method. The CD and FTIR studies showed that band 3-1a and band 3-1b in a membrane lipid bilayer cannot assume an alpha-helix rich structure but instead assume a beta-structure rich conformation. The proteolytic digestion experiments demonstrated that the cleavage sites of Tyr392 and Phe423 were common to both the model and erythrocyte membranes. Taken together with our previous work, which indicated that the first membrane-contact portion was the portion embedded in the erythrocyte membrane without tight lipid-peptide interactions [Hamasaki et al. (1997) J. Biochem. 122, 577-585], we imply herein that the first membrane-contact portion of band 3 by itself can not assume the ordinary alpha-helix conformation in the membrane lipid bilayers. A proteinase-resistant portion, from Ser402 to Phe423, was observed when liposomes containing band 3-1a were digested with proteinase K, while no proteinase-resistant core portion was found in the case of band 3-1b (DeltaAla400-Ala408). This suggests the crucial role of the deleted portion, from Ala400 to Ala408, in the interaction of the first membrane-contact portion of band 3 with a membrane lipid bilayer.