Phg, a novel member of the autotransporter family present in Bordetella species

Abstract

Several proteins encoded in the genomes of Bordetella species show significant sequence similarity to the autotransporter domains of surface exposed or secreted virulence factors of bordetellae such as pertactin, tracheal colonization factor or Vag8. One of these putative autotransporters, provisionally termed Phg, is encoded by the pertactin homologous gene (phg), which is highly conserved in Bordetella pertussis, B. bronchiseptica and B. parapertussis, but absent in B. avium and B. petrii. In contrast to homologues with documented functions in host interaction and virulence, several key amino acids probably involved in proteolytic processing of the autotransporter domain are not conserved in Phg. The transcription start site of phg was identified by primer extension analysis, but differential transcription of phg could not be detected in B. bronchiseptica strains under conditions that lead to enhanced expression of other known Bordetella autotransporter proteins. A mutant of B. pertussis was constructed in which major parts of phg are substituted by a kanamycin resistance cassette. Virulence testing of this mutant in a mouse respiratory infection model showed the same colonization properties as the wild-type strain.

Cleavage of a bacterial autotransporter by an evolutionarily convergent autocatalytic mechanism

“…Previous work has shown that the cleavage of the passenger domains of several members of the pertactin (Prn) family of autotransporters produced by B. pertussis occurs after an asparagine residue (Middendorf et al , 2005). While the β domains of these proteins are closely related to each other, they are only weakly related to the β domains of the SPATEs (Figure 1).…”

Acquisition of C1 inhibitor by Bordetella pertussis virulence associated gene 8 results in C2 and C4 consumption away from the bacterial surface

“…The C-terminus of Vag8 has high sequence identity to other B . pertussis autotransporter proteins including Prn [ 40 ]. Previous data indicated that unlike most autotransporters [ 41 , 42 ], the passenger domain of Vag8 would not be cleaved [ 5 ].…”