The porins from the halophilic species Ectothiorhodospira shaposhnikovii and Ectothiorhodospira vacuolata.
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.
Wolf
E
E
Institut für Biologie II, Mikrobiologie, Albert-Ludwigs-Universität, Schänzlestrasse 1, D-79104 Freiburg, Germany.
Zahr
M
M
Benz
R
R
Imhoff
J F
JF
Lustig
A
A
Schiltz
E
E
Stahl-Zeng
J
J
Weckesser
J
J
D000595:Amino Acid Sequence; D001419:Bacteria / Q000378:metabolism*; D008969:Molecular Sequence Data; D018272:Porins / Q000737:chemistry / Q000302:isolation & purification*
D018272:Porins