Miguel Rubio

Characterization of the Response to Zinc Deficiency in the Cyanobacterium Anabaena sp. Strain PCC 7120

Zur regulators control zinc homeostasis by repressing target genes under zinc-sufficient conditions in a wide variety of bacteria. This paper describes how part of a survey of duplicated genes led to the identification of the open reading frame all2473 as the gene encoding the Zur regulator of the cyanobacterium Anabaena sp. strain PCC 7120. All2473 binds to DNA in a zinc-dependent manner, and its DNA-binding sequence was characterized, which allowed us to determine the relative contribution of particular nucleotides to Zur binding. A zur mutant was found to be impaired in the regulation of zinc homeostasis, showing sensitivity to elevated concentrations of zinc but not other metals. In an effort to characterize the Zur regulon in Anabaena, 23 genes containing upstream putative Zur-binding sequences were identified and found to be regulated by Zur. These genes are organized in six single transcriptional units and six operons, some of them containing multiple Zur-regulated promoters. The identities of genes of the Zur regulon indicate that Anabaena adapts to conditions of zinc deficiency by replacing zinc metalloproteins with paralogues that fulfill the same function but presumably with a lower zinc demand, and with inducing putative metallochaperones and membrane transport systems likely being involved in the scavenging of extracellular zinc, including plasma membrane ABC transport systems and outer membrane TonB-dependent receptors. Among the Zur-regulated genes, the ones showing the highest induction level encode proteins of the outer membrane, suggesting a primary role for components of this cell compartment in the capture of zinc cations from the extracellular medium.

Highly enantioselective hydrogenation of enol ester phosphonates catalyzed by rhodium phosphine-phosphite complexes

Chiral phosphine-phosphites provide versatile catalysts for the highly enantioselective hydrogenation of alpha-acyloxy alpha, beta-unsaturated phosphonates.

Rhodium-catalyzed, efficient deutero- and tritiosilylation of carbonyl compounds from hydrosilanes and deuterium or tritium.

A cationic rhodium compound which is an active catalyst for both the hydrogen isotope exchange in hydrosilanes and the hydrosilylation of carbonyl compounds permits, in a one-flask, two-step procedure, efficient deutero- and tritiosilylations using SiEt(3)H under D(2) (0.5 bar) or T(2), at low catalyst loadings (0.1-0.5 mol %).

Rhodium diphosphite pincer complexes. Rare preferred in-plane olefin conformation in square-planar compounds

Square-planar ethylene rhodium derivatives bearing pincer diphosphite ligands have been prepared and characterized, they display a rare in-plane coordination which, based on DFT calculations, has been mainly attributed to steric effects.