S. Guedin et al., Novel topological features of FhaC, the outer membrane transporter involved in the secretion of the Bordetella pertussis filamentous hemagglutinin, J BIOL CHEM, 275(39), 2000, pp. 30202-30210
Many pathogenic Gram-negative bacteria secrete virulence factors across the
cell envelope into the extracellular milieu. The secretion of filamentous
hemagglutinin (FHA) by Bordetella pertussis depends on the pore-forming out
er membrane protein FhaC, which belongs to a growing family of protein tran
sporters. Protein alignment and secondary structure predictions indicated t
hat FhaC is likely to be a beta-barrel protein with an odd number of transm
embrane beta-strands connected by large surface loops and short periplasmic
turns. The membrane topology of FhaC was investigated by random insertion
of the c-Myc epitope and the tobacco etch virus protease-specific cleavage
sequence. FhaC was fairly permissive to short linker insertions. Furthermor
e, FhaC appeared to undergo conformational changes upon FHA secretion. Surf
ace detection of the inserted sequences indicated that several predicted lo
ops in the C-terminal moiety as well as the N terminus of the protein are e
xposed. However, a large surface-predicted region in the N-terminal moiety
of FhaC was inaccessible from the surface. In addition, the activity and th
e stability of the protein were affected by insertions in that region, indi
cating that it may have important structural and/or functional roles. The s
urface exposure of the N terminus and the presence of an odd number of beta
-strands are novel features for beta-barrel outer membrane proteins.