Structural divergence of paralogous S components from ECF-type ABC transporters.
Energy coupling factor (ECF) proteins are ATP-binding cassette transporters involved in the import of micronutrients in prokaryotes. They consist of two nucleotide-binding subunits and the integral membrane subunit EcfT, which together form the ECF module and a second integral membrane subunit that captures the substrate (the S component). Different S components, unrelated in sequence and specific for different ligands, can interact with the same ECF module. Here, we present a high-resolution crystal structure at 2.1 Å of the biotin-specific S component BioY from Lactococcus lactis. BioY shares only 16% sequence identity with the thiamin-specific S component ThiT from the same organism, of which we recently solved a crystal structure. Consistent with the lack of sequence similarity, BioY and ThiT display large structural differences (rmsd = 5.1 Å), but the divergence is not equally distributed over the molecules: The S components contain a structurally conserved N-terminal domain that is involved in the interaction with the ECF module and a highly divergent C-terminal domain that binds the substrate. The domain structure explains how the S components with large overall structural differences can interact with the same ECF module while at the same time specifically bind very different substrates with subnanomolar affinity. Solitary BioY (in the absence of the ECF module) is monomeric in detergent solution and binds D-biotin with a high affinity but does not transport the substrate across the membrane.
Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, Netherlands Proteomics Centre, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Ronnie P-A
RP
Berntsson
Josy
J
ter Beek
Maria
M
Majsnerowska
Ria H
RH
Duurkens
Pranav
P
Puri
Bert
B
Poolman
Dirk-Jan
DJ
Slotboom
D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D001710:Biotin / Q000378:metabolism*; D018360:Crystallography, X-Ray; D007700:Kinetics; D013294:Lactococcus lactis / Q000378:metabolism*; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D014815:Vitamins / Q000378:metabolism
D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D008081:Liposomes; D014815:Vitamins; D001710:Biotin