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 [PI] = 61.0%) 9.00-dalton N-terminal 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 apolipoprotein A1 (surface lipid-associating domain). The second domain is located in the highly hydrophobic (PI = 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 (PI = 53.8%) does not show structural similarity with lipid-associating domains.
Primary structure of diphtheria toxin fragment B: structural similarities with lipid-binding domains.
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P Lambotte, P Falmagne, C Capiau, J Zanen, J M Ruysschaert, J Dirkx; Primary structure of diphtheria toxin fragment B: structural similarities with lipid-binding domains.. J Cell Biol 1 December 1980; 87 (3): 837–840. doi: https://doi.org/10.1083/jcb.87.3.837
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