Crystal structure of a copper-transporting PIB-type ATPase

Heavy-metal homeostasis and detoxification is crucial for cell viability. P-type ATPases of the class IB (PIB) are essential in these processes, actively extruding heavy metals from the cytoplasm of cells. Here we present the structure of a PIB-ATPase, a Legionella pneumophila CopA Cu(+)-ATPase, in a copper-free form, as determined by X-ray crystallography at 3.2 ? resolution. The structure indicates a three-stage copper transport pathway involving several conserved residues. A PIB-specific transmembrane helix kinks at a double-glycine motif displaying an amphipathic helix that lines a putative copper entry point at the intracellular interface. Comparisons to Ca(2+)-ATPase suggest an ATPase-coupled copper release mechanism from the binding sites in the membrane via an extracellular exit site. The structure also provides a framework to analyse missense mutations in the human ATP7A and ATP7B proteins associated with Menkes' and Wilson's diseases.     

Light stimulates growth of proteorhodopsin-containing marine Flavobacteria

Proteorhodopsins are bacterial light-dependent proton pumps. Their discovery within genomic material from uncultivated marine bacterioplankton caused considerable excitement because it indicated a potential phototrophic function within these organisms, which had previously been considered strictly chemotrophic. Subsequent studies established that sequences encoding proteorhodopsin are broadly distributed throughout the world's oceans. Nevertheless, the role of proteorhodopsins in native marine bacteria is still unknown. Here we show, from an analysis of the complete genomes of three marine Flavobacteria, that cultivated bacteria in the phylum Bacteroidetes, one of the principal components of marine bacterioplankton, contain proteorhodopsin. Moreover, growth experiments in both natural and artificial seawater (low in labile organic matter, which is typical of the world's oceans) establish that exposure to light results in a marked increase in the cell yield of one such bacterium (Dokdonia sp. strain MED134) when compared with cells grown in darkness. Thus, our results show that the phototrophy conferred by proteorhodopsin can provide critical amounts of energy, not only for respiration and maintenance but also for active growth of marine bacterioplankton in their natural environment.     

The nonlinear nature of friction

Tribology is the study of adhesion, friction, lubrication and wear of surfaces in relative motion. It remains as important today as it was in ancient times, arising in the fields of physics, chemistry, geology, biology and engineering. The more we learn about tribology the more complex it appears. Nevertheless, recent experiments coupled to theoretical modelling have made great advances in unifying apparently diverse phenomena and revealed many subtle and often non-intuitive aspects of matter in motion, which stem from the nonlinear nature of the problem.