Identification of Secretion Determinants of the Bordetella pertussis BrkA Autotransporter

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American Society for Microbiology

RESUMO

The autotransporters comprise a functionally diverse family of gram-negative proteins that mediate their own export across the bacterial outer membrane. They consist of an amino-terminal passenger region called the “α-domain” and the structural hallmark of the autotransporter family, a carboxy-terminal transporter region usually referred to as the “β-domain.” The passenger region can be quite diverse and constitutes the effector functions of these proteins, whereas the C-terminal region is conserved and is responsible for translocating the passenger moiety across the outer membrane. BrkA is the 103-kDa autotransporter protein in Bordetella pertussis that is cleaved to yield a 73-kDa N-terminal α-domain and a 30-kDa C-terminal β-domain. We have previously shown that a recombinant form of the β-domain of BrkA is capable of forming channels in artificial membranes. Here, we define two additional secretion determinants of BrkA. N-terminal sequencing of the 73-kDa BrkA passenger from B. pertussis and Escherichia coli revealed that BrkA has a 42-amino-acid signal peptide. In addition, deletion analysis of BrkA identified a 31- to 39-amino-acid region found immediately upstream of the β-domain that was essential for surface expression. This 31- to 39-amino-acid linker region, together with the β-domain, defines the minimal BrkA translocation unit. The linker region may also serve to anchor the BrkA passenger to the bacterial surface.

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