Primary structure of diphtheria toxin fragment B: Structural similarities with lipid-binding domains

Abstract

Two different lipid-associating domains have been identified in the B fragment of diphtheria toxin using automated Edman degradation of its cyanogen bromide peptides, secondary structure prediction analysis, and comparisons with known phospholipid-interacting proteins. The first domain is located in the highly hydrophilic (polarity index [Pl] = 61.0%) 9,000-dalton Nterminal region of fragment B. This region shows primary and predicted secondary structures dramatically similar to those found for the phospholipid headgroup-binding domains of human apolípoprotein A1 (surface lipid-associating domain). The second domain is located in the highly hydrophobic (Pl = 32.4%) middle region of fragment B. Its structure resembles that found for the membranous domain of intrinsic membrane proteins (transverse lipid-associating domain). In contrast, the hydrophilic C-terminal 8,000-dalton region of fragment B (Pl = 53.8%) does not show structural similarity with lipid-associating domains. © 1980, Rockefeller University Press., All rights reserved.