RESUMO
Potassium channels allow K+ to rapidly diffuse, while the selectivity filter (SF) actively blocks Na+. The presence of water in the SF during ion translocation remains under debate due to the experimental and computational challenges in characterizing the interactions between water, ions, and the SF. Our bottom-up approach has been applied to a system composed of a partial peptide of the SF (Ac-tyrosine-NHMe) with a metal ion and a single water molecule to probe these interactions. The IR photodissociation spectra of M+Ac-tyrosine-NHMe(H2O) (M = Na, K) combined with quantum chemical calculations revealed that the water molecule binding sites are ion-dependent. In addition, the ion-peptide distances are elongated significantly for the K+ complex in comparison to the Na+ complex by the addition of a single water molecule. This striking structural difference with the water molecule is discussed in relation to ion selectivity and translocation within the K+ channel.
RESUMO
A cellulolytic and agarolytic bacterial strain, designated 12-2T, was isolated from a piece of cotton rope fragment washed ashore on a beach and was studied phenotypically, genotypically and phylogenetically. Analyses of 16S rRNA and gyrB gene sequences and DNA base composition suggested that the strain is a member of the genus Gilvimarinus. However, levels of 16S rRNA and gyrB gene sequence similarity between it and the type strains of Gilvimarinus species were no higher than 97.9 and 78.7 %, respectively, suggesting that the strain is distinct. Moreover, the results of DNA-DNA hybridization experiments and physiological characterization clearly differentiated the strain from its closest neighbours. The strain is therefore considered to represent a novel species of the genus Gilvimarinus, for which the name Gilvimarinus japonicus sp. nov. is proposed. The type strain is 12-2T (=NBRC 111987T=KCTC 52141T).