Substrate-Induced Conformational Changes in the S-Component ThiT from an Energy Coupling Factor Transporter

• Published in: Structure (London) Vol. 21; no. 5; pp. 861 - 867
• Main Authors: Majsnerowska, Maria, Hänelt, Inga, Wunnicke, Dorith, Schäfer, Lars V., Steinhoff, Heinz-Jürgen, Slotboom, Dirk Jan
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 07-05-2013
• Subjects: ATP-Binding Cassette Transporters - chemistry; ATP-Binding Cassette Transporters - metabolism; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Binding; Binding Sites; Crystallography, X-Ray; Joining; Lactococcus lactis - metabolism; Membrane Proteins - chemistry; Membrane Proteins - metabolism; Membranes; Models, Molecular; Prokaryotes; Protein Structure, Tertiary; Proteins; Spectrometry, Fluorescence; Spectroscopy; Thiamine - chemistry; Thiamine - metabolism; Transporter; Vitamins
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2013.03.007

Energy coupling factor (ECF) transporters are a recently discovered class of ABC transporters that mediate vitamin uptake in prokaryotes. Characteristic for ECF-type ABC transporters are small integral membrane proteins (S-components) that bind the transported substrates with high affinity. S-components associate with a second membrane protein (EcfT) and two peripheral ATPases to form a complete ATP-dependent transporter. Here, we have used EPR spectroscopy, stopped-flow fluorescence spectroscopy, and molecular dynamics simulations to determine the structural rearrangements that take place in the S-component ThiT from Lactococcus lactis upon binding of thiamin. Thiamin-induced conformational changes were confined to the long and partially membrane-embedded loop between transmembrane helices 1 and 2 that acts as a lid to occlude the binding site. The results indicate that solitary ThiT functions as a bona fide high-affinity substrate binding protein, which lacks a translocation pathway within the protein.
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•Binding of thiamin to ThiT requires opening of lid-like loop 1-2•The transmembrane helices form a rigid scaffold•A translocation path for thiamin transport is absent in solitary ThiT
S-components are small integral membrane proteins that bind transported substrates in ECF-type ABC transporters. Majsnerowska et al. show that binding of thiamin to the S-components ThiT requires opening of lid-like loop 1-2 that occludes the binding site, with transmembrane helices forming a rigid scaffold.