Biomedical subjects

Juan A Fuentes

Publications and source records attributed to Juan A Fuentes.

4 recordsLinked to original sources

PubMed2006

The cotranscribed Salmonella enterica sv. Typhi tsx and impX genes encode opposing nucleoside-specific import and export proteins.

The Salmonella enterica tsx gene encodes a nucleoside-specific outer membrane channel. The Tsx porin is essential for the prototrophic growth of S. enterica sv. Typhi in the absence of nucleosides. RT-PCR analysis shows that the tsx gene is cotranscribed with an open reading frame unique to S. enterica, impX (STY0450), which encodes an inner membrane protein 108 amino acids in length, which is predicted to have only two transmembrane alpha-helices. Fusions of the lacZ gene to both tsx and impX reveal that the transcription of both genes is induced in the presence of adenosine. A null mutation in the S. Typhi impX gene suppresses the induced auxotrophy for adenosine or thymidine resulting from a tsx mutation and confers sensitivity to high concentrations of adenosine or thymidine. The ImpX protein, when tagged with a 3xFLAG epitope, is functional and associates with the inner membrane; impX mutants are defective in the export of 3H-radiolabeled thymidine. Taken together, these and other results suggest that the S. Typhi Tsx porin and ImpX inner membrane protein facilitate competing mechanisms of thymidine influx and efflux, respectively, to maintain the steady-state levels of internal nucleoside pools.

Adenosine↗

PubMed2004

Precise excision of the large pathogenicity island, SPI7, in Salmonella enterica serovar Typhi.

The large pathogenicity island (SPI7) of Salmonella enterica serovar Typhi is a 133,477-bp segment of DNA flanked by two 52-bp direct repeats overlapping the pheU (phenylalanyl-tRNA) gene, contains 151 potential open reading frames, and includes the viaB operon involved in the synthesis of Vi antigen. Some clinical isolates of S. enterica serovar Typhi are missing the entire SPI7, due to its precise excision; these strains have lost the ability to produce Vi antigen, are resistant to phage Vi-II, and invade a human epithelial cell line more rapidly. Excision of SPI7 occurs spontaneously in a clinical isolate of S. enterica serovar Typhi when it is grown in the laboratory, leaves an intact copy of the pheU gene at its novel join point, and results in the same three phenotypic consequences. SPI7 is an unstable genetic element, probably an intermediate in the pathway of lateral transfer of such pathogenicity islands among enteric gram-negative bacteria.

Antigens, Bacterial↗

PubMed2003

Prophage contribution to bacterial population dynamics.

Cocultures of Salmonella strains carrying or lacking specific prophages undergo swift composition changes as a result of phage-mediated killing of sensitive bacteria and lysogenic conversion of survivors. Thus, spontaneous prophage induction in a few lysogenic cells enhances the competitive fitness of the lysogen population as a whole, setting a selection regime that forces maintenance and spread of viral DNA. This is likely to account for the profusion of prophage sequences in bacterial genomes and may contribute to the evolutionary success of certain phylogenetic lineages.

Biological Evolution↗

PubMed2002

The Salmonella enterica sv. Typhimurium smvA, yddG and ompD (porin) genes are required for the efficient efflux of methyl viologen.

In Gram-negative bacteria, a subset of inner membrane proteins in the major facilitator superfamily (MFS) acts as efflux pumps to decrease the intracellular concentrations of multiple toxic substrates and confers multidrug resistance. The Salmonella enterica sv. Typhimurium smvA gene encodes a product predicted to be an MFS protein most similar to QacA of Staphylococcus aureus. Like mutations in qacA, mutations in smvA confer increased sensitivity to methyl viologen (MV). Mutations in the adjacent ompD (porin) and yddG (drug/metabolite transporter) genes also confer increased sensitivity to MV, and mutations in smvA are epistatic to mutations in ompD or yddG for this phenotype. YddG and OmpD probably comprise a second efflux pump in which the OmpD porin acts as an outer membrane channel (OMC) protein for the efflux of MV and functions independently of the SmvA pump. In support of this idea, the pump dependent on YddG and OmpD has a different substrate specificity from the pump dependent on SmvA. Mutations in tolC, which encodes an OMC protein, confer increased resistance to MV. TolC apparently facilitates the import of MV, and a subset of OMC proteins including the OmpD porin and TolC may facilitate both import and export of distinct subsets of toxic substrates.

Amino Acid Sequence↗