B Dargent — Page 2 | PubMed Health

PubMed1987

Selectivity for maltose and maltodextrins of maltoporin, a pore-forming protein of E. coli outer membrane.

Homogenous maltoporin (lamB protein), an Escherichia coli outer membrane spanning protein, was incorporated in phospholipid planar bilayers. It generates aqueous channels distinct from those formed by the non-specific porin (OmpF) or by phosphoporin (phoE protein). The single conductance, 150 pS in 1 M NaCl, is much smaller than that of the porins. The channels, which are poorly selective for cations and voltage independent, are specifically inhibited by maltose and maltodextrins. This inhibition, observed in the absence of maltose binding protein, demonstrates that the selectivity of maltoporin for maltose and maltodextrins is an intrinsic property of the protein.

Bacterial Outer Membrane Proteins↗

PubMed1986

The selectivity filter of voltage-dependent channels formed by phosphoporin (PhoE protein) from E. coli.

Phosphoporin, an Escherichia coli outer membrane-spanning protein re-incorporated in phospholipid planar bilayers generates aqueous channels similar to those of matrix porin. One phosphoporin trimer contains three pores which are induced simultaneously but fluctuate separately between open and closed states. Membrane potential shifts this two-state equilibrium in favour of closed channels. This negative resistance occurs at lower potentials than with matrix porin channels. The phosphoporin channel is poorly anion selective for small solutes. Polyphosphates and other phosphorylated molecules specifically inhibit phosphoporin pore conductance to small ions, a property which is specific to phosphoporin. There is an excellent correlation between the effect of such solutes measured in planar bilayers and their inhibitory effect on beta-lactam antibiotic uptake in vivo by phosphoporin. It is concluded that the phosphoporin channel contains a selectivity filter which is only efficient for larger molecules, most probably through basic residues.

Adenosine Triphosphate↗