Conductance of OmpA [outer membrane protein A] small and large channels

Range more frequent smaller channel 50-80pS: less frequent larger channel 260-320pS picosiemens
Organism Bacteria Escherichia coli
Reference Arora A, Rinehart D, Szabo G, Tamm LK. Refolded outer membrane protein A of Escherichia coli forms ion channels with two conductance states in planar lipid bilayers. J Biol Chem. 2000 Jan 21 275(3):1594-600. abstract, p.1595 left column 3rd paragraph & p.1598 right column 2nd paragraphPubMed ID10636850
Method Abstract:"[Investigators] have incorporated detergent-purified OmpA into planar lipid bilayers and studied its permeability to ions by single channel conductance measurements."
Comments Abstract:"In 1 M KCl, OmpA formed small (50-80 pS) and large (260-320 pS) channels. These two conductance states were interconvertible, presumably corresponding to two different conformations of OmpA in the membrane. The smaller channels are associated with the N-terminal transmembrane domain, whereas both domains are required to form the larger channels." P.1595 left column 3rd paragraph:"Because the formation of ion channels by OmpA has not been universally accepted and to develop a practical assay for the refolding of OmpA, [investigators] re-investigated the channel activity of OmpA in a well defined reconstituted lipid bilayer system. [They] found that both native OmpA and OmpA that was refolded in the detergent C8E4forms two types of ion-conducting channels in planar bilayer membranes. The more frequent smaller channels exhibited a conductance of 50–80 pS and the less frequent larger channels a conductance of 260–320 pS in 1m KCl at a 100 mV membrane potential. The smaller but not the larger conductance state was also observed when the N-terminal transmembrane domain, i.e. a fragment comprising residues 1–176, was refolded and incorporated into planar lipid bilayers. Five single tryptophan mutants of OmpA exhibited small and large channel conductances similar to those of wild-type OmpA."
Entered by Uri M
ID 112277