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On the role of the two extracytoplasmic substrate‐binding domains in the ABC transporter OpuA
Author(s) -
BiemansOldehinkel Esther,
Poolman Bert
Publication year - 2003
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/cdg581
Subject(s) - biology , atp binding cassette transporter , transporter , substrate specificity , plasma protein binding , genetics , computational biology , microbiology and biotechnology , biochemistry , gene , enzyme
Members of two transporter families of the ATP‐binding cassette (ABC) superfamily use two or even four extracytoplasmic substrate‐binding domains (SBDs) for transport. We report on the role of the two SBDs in the translocation cycle of the ABC transporter OpuA from Lactococcus lactis . Heterooligomeric OpuA complexes with only one SBD or one functional and one non‐functional SBD (inactivated by covalent linkage of a substrate mimic) have been constructed, and the substrate binding and transport kinetics of the purified transporters, reconstituted in liposomes, have been determined. The data indicate that the two SBDs of OpuA interact in a cooperative manner in the translocation process by stimulating either the docking of the SBDs onto the translocator or the delivery of glycine betaine to the translocator. It appears that one of these initial steps, but not the later steps in translocation or resetting of the system to the initial state, is rate determining for transport. These new insights on the functional role of the extracytoplasmic SBDs are discussed in the light of the current knowledge of substrate‐binding‐protein‐dependent ABC transporters.