MEMBRANE ASSEMBLY OF CIRCULARLY PERMUTED VARIANTS OF THE ESCHERICHIA-COLI OUTER-MEMBRANE PROTEIN OMPA

The two-domain, 325 residue outer membrane protein OmpA is one of the most abundant proteins of Escherichia coli, playing a role in the main tenance of the integrity of the cell surface. The N-terminal domain, c onsisting of about 170 amino acid residues, is embedded in the membran e, presumably in the form of a beta-barrel consisting of eight amphipa thic transmembrane strands. Pairs of these proposed transmembrane stra nds were permuted at the DNA level, in order to dissect the process of membrane assembly. All three possible circular permutations led to va riants, which were, in comparison with the wild-type protein, less eff iciently assembled. In contrast, no membrane assembly could be detecte d in any of 18 non-circularly permuted variants. We take this as an in dication that the ''right'' (wild-type) order of beta-strands is a nec essary and sufficient prerequisite for at least partially successful m embrane assembly This may be the consequence of packing constraints an d/or a failure to adopt the wild-type arrangement of beta-strands, whi ch require crossing of the periplasmic turns. (C) 1995 Academic Press Limited