A novel bacterial ATP-binding cassette transporter system that allows uptake of macromolecules

A gram-negative bacterium, Sphingomonas sp. strain A1, isolated as a produc er of alginate lyase, has a characteristic cell envelope structure and form s a mouth-like pit on its surface. The pit is produced only when the cells have to incorporate and assimilate alginate. An alginate uptake-deficient m utant was derived from cells of strain A1. One open reading frame, algS (1, 089 bp), exhibiting homology to the bacterial ATP-binding domain of an ABC transporter, was cloned as a fragment complementing the mutation, algS was followed by two open reading frames, algM1 (972 bp) and algM2 (879 bp), whi ch exhibit homology with the transmembrane permeases of ABC transporters. D isruption of algS of strain A1 resulted in the failure to incorporate algin ate and to form a pit. Hexahistidine-tagged AlgS protein (AlgS(His6)) overe xpressed in Escherichia coli and purified by Ni2+ affinity column chromatog raphy showed ATPase activity. Based on these results, we propose the occurr ence of a novel pit-dependent ABC transporter system that allows the uptake of macromolecules.