The porins from the halophilic species Ectothiorhodospira shaposhnikovii and Ectothiorhodospira vacuolata

Abstract

Major outer membrane proteins with porin activity were isolated from cell envelopes of the halophilic strains Ectothiorhodospira shaposhnikovii N1 and Ectothiorhodospira vacuolata beta1. The porins were obtained as oligomers. They dissociated into monomers by heat or EDTA treatment. The molecular masses of the monomers were determined by mass spectrometry to be 39,285 and 37,160 Da for E. shaposhnikovii N1 and E. vacuolata beta1, respectively. Both were shown by analytical ultracentrifugation to be trimers of about 112, 000 Da. Circular dichroism spectra indicated predominantly beta-sheet structure. The 18 N-terminal amino acid sequences of the two porins were identical except for the amino acids in positions 12 and 14. No sequence similarity with the primary structure of known porins was found. In reconstitution experiments with lipid bilayers, the porins of E. shaposhnikovii N1 and E. vacuolata beta1 formed channels with a single-channel conductance of 1.5 and 0.7 nS, respectively, in 1 M KCl. The single-channel conductance saturated with increasing salt concentration, indicating a putative binding-site for anions in the channel since both porins exhibited anion-selectivity. For the porin of E. vacuolata beta1, but not for that of E. shaposhnikovii N1, an influence of detergent concentration on the single-channel conductance was observed.

High‐resolution architecture of the outer membrane of the Gram‐negative bacteria Roseobacter denitrificans

“…, 1997). As this conductivity is characteristic for porins from halophilic species (Wolf et al. , 1996), it could be an evolutionary adaptation to deal with high salt concentration in the environment.…”

Molecular Basis of Bacterial Outer Membrane Permeability Revisited

“…A porin gene from Ectothiorhodospira, a halophilic photosynthetic organism, has been sequenced, but the sequence does not appear to resemble the sequence of genes encoding enterobacterial porins (742), again a reasonable result in view of the distance between the two branches. Porins from two other species, Ectothiorhodospira shaposhnikovii and E. vacuolata, were shown to be trimeric, anion-preferring porins with single-channel conductance values typical for classical trimeric porins (743).…”

Revision of species delineation in the genus Ectothiorhodospira.

“…Lipopolysaccharides of E. shaposhnikovii DSM 243 T and E. vacuolata DSM 2111 T are very similar and, in particular, a high degree of similarity is shown by the fatty acid composition of their lipid A moieties (Meißner et al, 1988 ;Zahr et al, 1992). In finding that porins of E. shaposhnikovii and E. vacuolata were unusually conserved, Wolf et al (1996) observed that they were actually more similar to each other than porins isolated from two bacterial strains belonging to the same species, Rhodobacter capsulatus. Other morphological and physiological characters, as summarized by the respective species descriptions given in Bergey's Manual of Systematic Bacteriology (Imhoff, 1989) are nearly identical ; minor differences can only be detected in cell diameter and nitrate assimilation.…”