Primary structure of major outer membrane protein I of Escherichia coli B/r.

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Abstract
The amino acid sequence of the pore-forming outer membrane protein I (porin) from E. coli B/r was determined. The polypeptide contains 340 amino acid residues resulting in a MW of 37,205. The transmembrane polypeptide has no stretches of nonpolar residues, uninterrupted by charged side chains, longer than 11 amino acid residues. Regarding polarity, the chain can be subdivided into 3 regions: a distinctly hydrophilic region between residues 1 and 82 (51.2% polarity), a fairly nonpolar region between residues 83 and 194 (33.9% polarity), and a more hydrophilic region up to the COOH terminus (48% polarity). These results are interpreted as evidence against a simple transmembrane structure in which the membrane is spanned by a single contiguous sequence of hydrophobic amino acids, as was proposed, e.g., for glycophorin.