COMPARATIVE ANALYSIS OF THE TWIN-ARGININE TRANSLOCATION PATHWAY IN ALPHAPROTEOBACTERIA

NUÑEZ P; MORETTA R; SORIA M; FARBER M

Institut Pasteur, Paris, Francia

Conferencia; Genome 2008. functional Genomics of Microorganism; 2008

Institut Pasteur de Paris

The alphaproteobacteria is a diverse class of Gram-negative bacteria that shows great genomic and biological variability representing an excellent model system for evolutionary and comparative studies. Particularly, protein export and traslocation systems acquire great relevance as they are implicated in bacterial virulence mechanism. The Twin Argininie traslocation pathway is a novel protein transport system that targets folded proteins across the inner membrane. The integral membrane proteins TAT A, B and C are essential components of the system. While TAT components have been identified the extent to which this secretory pathway is utilized in bacteria is not well characterized. Comparative genomic analysis was performed through out 25 alphaproteobacteria genome sequences. The presence of the three genes was confirmed in almost all studied genomes, with the exception of Ricketsia and Neorickettsia genus that lack tatB. Analyzing the synteny of the tatA, B, and C genes, it was possible to split the class into two groups, one with tatABC operon  and another one with an scattered structure. While tatC is highly conserved in all the studied genomes, tatA and B are truncated in Rickettsiales though maintaining the main structural domains. Moreover, critical amino acid residues are conserved among almost all the studied organisms. RT-PCR using RNA from A.marginale and B.abortus not only confirmed expression of tat genes, but also the operon transcription structure in the case of B. abortus. Assays for determining stoichiometric ratio of tat components  and the ability of heterologous tat genes to compensate for the absence of the cognate E. coli ones,  are in progress. In order to better to understand the biological and evolutive relevance of TAT system,genome-wide identification of putative tat substrates using TATFIND1.4 was performed. Some families  seem to have maintained the tat pathway for the secretion of only one tat substrate, since others like Bradyrhizobium japonicum, Mesorhizobium loti, Caulobacter crescentus appear to make extensive use of this pathway, as 122, 87, 81 putative tat substrates were identified, respectively.