Super-channel in bacteria: function and structure of the macromolecule import system mediated by a pit-dependent ABC transporter

In a soil isolate, Sphingomonas sp. A I, the transport of a macromolecule ( alginate: 27 kDa) is mediated by a pit-dependent ATP-binding cassette (ABC) transporter. The transporter is different from other ABC transporters so f ar analyzed in that its function is dependent on a pit, a mouth-like organ formed on the cell surface only when cells are compelled to assimilate macr omolecules, and in that it allows direct import of macromolecules into cell s. The ABC transporter coupled with the pit, which functions as a funnel an d/or concentrator of macromolecules to be imported, was designated the 'sup er-channel', and in this review, we discuss the three-dimensional structure and specific function of the 'super-channel' for macromolecule import foun d for the first time in a bacterium. (C) 2001 Federation of European Microb iological Societies. Published by Elsevier Science B.V. All rights reserved .