Permeability properties of Escherichia coli outer membrane containing, pore-forming proteins: comparison between lambda receptor protein and porin for saccharide permeation.

AUTOR(ES)

Nakae, T

RESUMO

Outer membrane permeability conferred by lambda receptor protein and porins to maltose-maltodextrins and other oligosaccharides was studied in vitro with reconstituted vesicle membranes and in vivo with mutant strains lacking either one of these proteins. The vesicle membranes reconstituted from phospholipids, lipopolysaccharide, and purified lambda receptor allowed rapid diffusion of maltose and maltose-maltodextrins of up to six glucose residues, but the membranes acted essentially as a molecular sieve for sucrose, raffinose, stachyose, and inulins of molecular weights 800, 920, and 1,380. The vesicle membranes containing porins allowed rapid diffusion of maltose but not of maltose-maltodextrins larger than maltose. The apparent transport Km values for maltose-maltodextrins of up to six glucose residues from the strain carrying lamB+ ompB (lambda receptor+, porin-) were similar (about 5 X 10(-6) M), whereas the transport Km values for maltose- and maltotriose of the strain carrying lamB ompB+ (lambda receptor-, porin+) alleles appeared to be 300 and about 20,000 X 10(-6) M. These results suggest that lambda receptor protein forms permeability pores that facilitate the diffusion of maltose-maltodextrins and function as a molecular sieve for other saccharides.

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