Biomedical subjects

M Wexler

Publications and source records attributed to M Wexler.

At least 19 recordsLinked to original sources

PubMed2003

Fur is not the global regulator of iron uptake genes in Rhizobium leguminosarum.

Rhizobium leguminosarum fur mutants were unaffected in Fe-dependent regulation of several operons that specify different Fe uptake systems, yet cloned R. leguminosarum fur partially corrected an Escherichia coli fur mutant and R. leguminosarum Fur protein bound to canonical fur boxes. The lack of a phenotype in fur mutants is not due to functional redundancy with Irr, another member of the Fur superfamily found in the rhizobia, since irr fur double mutants are also unaffected in Fe-responsive regulation of several operons involved in Fe uptake. Neither Irr nor Fur is needed for symbiotic N(2) fixation on peas. As in Bradyrhizobium japonicum, irr mutants accumulated protoporphyrin IX. R. leguminosarum irr is not regulated by Fur and its Irr protein lacks the motif needed for haem-dependent post-translational modification that occurs in B. japonicum Irr. The similarities and differences in the Fur superfamily in the rhizobia and other Gram-negative bacteria are discussed.

Aldehyde Oxidoreductases↗

PubMed2002

Structural studies of the Fur protein from Rhizobium leguminosarum.

The X-ray crystal structure of the apo-form of the Fur protein from Rhizobium leguminosarum has been solved at 2.7 A resolution. Small-angle X-ray scattering was used to give information on the solution conformation of the protein. The Fur homodimer folds into two domains. The N-terminal domain is formed from the packing of two helix-turn-helix motifs while the C-terminal domain appears primarily to stabilize the dimeric state of the protein.

Amino Acid Sequence↗

PubMed2002

The vbs genes that direct synthesis of the siderophore vicibactin in Rhizobium leguminosarum: their expression in other genera requires ECF sigma factor RpoI.

A cluster of eight genes, vbsGSO, vbsADL, vbsC and vbsP, are involved in the synthesis of vicibactin, a cyclic, trihydroxamate siderophore made by the symbiotic bacterium Rhizobium leguminosarum. None of these vbs genes was required for symbiotic N2 fixation on peas or Vicia. Transcription of vbsC, vbsGSO and vbsADL (but not vbsP) was enhanced by growth in low levels of Fe. Transcription of vbsGSO and vbsADL, but not vbsP or vbsC, required the closely linked gene rpoI, which encodes an ECF sigma factor of RNA polymerase. Transfer of the cloned vbs genes, plus rpoI, to Rhodobacter, Paracoccus and Sinorhizobium conferred the ability to make vicibactin on these other genera. We present a biochemical genetic model of vicibactin synthesis, which accommodates the phenotypes of different vbs mutants and the homologies of the vbs gene products. In this model, VbsS, which is similar to many non-ribosomal peptide synthetase multienzymes, has a central role. It is proposed that VbsS activates L-N5-hydroxyornithine via covalent attachment as an acyl thioester to a peptidyl carrier protein domain. Subsequent VbsA-catalysed acylation of the hydroxyornithine, followed by VbsL-mediated epimerization and acetylation catalysed by VbsC, yields the vicibactin subunit, which is then trimerized and cyclized by the thioesterase domain of VbsS to give the completed siderophore.

Bacterial Proteins↗

PubMed2001