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Molecular analysis of an outer membrane protein, MopB, of Methylococcus capsulatus (Bath) and structural comparisons with proteins of the OmpA family

Fjellbirkeland, Anne, Bemanian, Vahid, McDonald, Ian R., Murrell, J. Colin, Jensen, Harald B.
Archives of microbiology 2000 v.173 no.5-6 pp. 346-351
DNA, Methylococcus capsulatus, Methylomonas methanica, Pseudomonas aeruginosa, databases, fluorescent labeling, genes, open reading frames, outer membrane proteins, polypeptides, sequence homology, signal peptide
The gene encoding a major outer membrane protein (MopB) of the methanotroph Methylococcus capsulatus (Bath) was cloned and sequenced. The cloned DNA contained an open reading frame of 1044 bp coding for a 348-amino-acid polypeptide with a 21-amino-acid leader peptide. Comparative sequence analysis of the predicted amino acid sequence revealed that the C-terminal part of MopB possessed sequences that are conserved in the OmpA family of proteins. The N-terminal half of the protein had no significant sequence similarity to other proteins in the databases, but the predicted secondary structure showed stretches of amphipathic β-strands typical of transmembrane segments of outer membrane proteins. A region with four cysteines similar to the cysteine-encompassing region of the OprF of Pseudomonas aeruginosa was found toward the C-terminal part of MopB. Results from whole-cell labeling with the fluorescent thiol-reacting reagent 5-iodoacetamidofluorescein indicated a surface-exposed location for these cysteines. A probe consisting of the 3′-end of the mopB gene hybridized to the type I methanotroph Methylomonas methanica S1 in Southern blots containing DNA from nine methanotrophic strains representing six different genera.