PRIMARY STRUCTURE OF MAJOR OUTER-MEMBRANE PROTEIN-I OF ESCHERICHIA-COLI B-R

The amino acid sequence of the pore-forming outer membrane protein I (porin) from E. coli B/r has been determined. The polypeptide contains 340 amino acid residues resulting in a molecular weight 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 three regions a distinctly hydrophilic region between residues 1 and 82 (51.2% polarity), a fairly nonpolar region betwen 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 has been proposed, for example, for glycophorin.