RESUMO
The type VI secretion system (T6SS) is recognized as an important virulence mechanism in several Gram-negative pathogens. In Vibrio cholerae, the causative agent of the diarrheal disease cholera, a minimum of three gene clusters--one main cluster and two auxiliary clusters--are required to form a functional T6SS apparatus capable of conferring virulence toward eukaryotic and prokaryotic hosts. Despite an increasing understanding of the components that make up the T6SS apparatus, little is known about the regulation of these genes and the gene products delivered by this nanomachine. VasH is an important regulator of the V. cholerae T6SS. Here, we present evidence that VasH regulates the production of a newly identified protein, VasX, which in turn requires a functional T6SS for secretion. Deletion of vasX does not affect export or enzymatic function of the structural T6SS proteins Hcp and VgrG-1, suggesting that VasX is dispensable for the assembly of the physical translocon complex. VasX localizes to the bacterial membrane and interacts with membrane lipids. We present VasX as a novel virulence factor of the T6SS, as a V. cholerae mutant lacking vasX exhibits a phenotype of attenuated virulence toward Dictyostelium discoideum.
Assuntos
Sistemas de Secreção Bacterianos , Dictyostelium , Vibrio cholerae/patogenicidade , Fatores de Virulência/metabolismo , Sistemas de Secreção Bacterianos/genética , Regulação Bacteriana da Expressão Gênica , Espectrometria de Massas , Lipídeos de Membrana/metabolismo , Reação em Cadeia da Polimerase , Estrutura Terciária de Proteína , Deleção de Sequência , Vibrio cholerae/genética , Vibrio cholerae/metabolismo , Fatores de Virulência/química , Fatores de Virulência/genéticaRESUMO
A number of prominent Gram-negative bacteria use the type VI secretion system (T6SS) to transport proteins across the bacterial envelope. Rapid progress is being made in elucidating the structural components of the T6SS apparatus, and a few effectors have been reported to pass through it. However, this is not the complete story: a family of T6SS proteins, the VgrGs, share structural features with the cell-puncturing device of the T4 bacteriophage, and may be used in a similar fashion by bacteria to puncture host cell membranes and insert the T6SS apparatus into the host cytosol. Interestingly, a number of VgrGs contain C-terminal extensions with effector-domains. Thus, the T6SS may translocate soluble effectors, as well as VgrG effector-domains.