PURIFICATION, AMINO-ACID-COMPOSITION, AND N-TERMINAL SEQUENCE OF THE MAJOR PROTEIN (PROTEIN-H) OF THE OUTER-MEMBRANE OF PASTEURELLA-MULTOCIDA

The major protein (protein H) of the outer membrane of Pasteurella mul tocida was purified by size-exclusion chromatography after selective e xtraction with detergents. The protein forms homotrimers which are sta ble in the presence of SDS at room temperature. Upon treatment at 100- degrees-C, the protein is fully dissociated by the detergent into mono mers exhibiting an apparent molecular mass of 37 kDa as estimated by e lectrophoresis. The amino acid composition of protein H is characteriz ed by a low hydropathy index (HI = -0.40) and is strongly related to t he compositions of bacterial porins, notably porins P2 (Haemophilus in fluenzae), PIA (Neisseria gonorrhoeae) and Cl.2 ("class 2 porin" of N. meningitidis). The N-terminal amino acid sequence of protein H shares a strong homology with those of porins OmpC (Escherichia coli) and P2 . These data indicate that protein H of P. multocida is a porin belong ing to the superfamily of the non-specific porins of Gram-negative eub acteria outer membrane.