Structure of a bacterial energy-coupling factor transporter

Tingliang Wang, Guobin Fu, Xiaojing Pan, Jianping Wu, Xinqi Gong, Jiawei Wang & Yigong Shi

Nature | Letter

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Structure of a bacterial energy-coupling factor transporter

Tingliang Wang,
Guobin Fu,
Xiaojing Pan,
Jianping Wu,
Xinqi Gong,
Jiawei Wang
& Yigong Shi

Nature 497, 272–276 (09 May 2013)
doi:10.1038/nature12045

Received 15 August 2012
Accepted 26 February 2013
Published online 14 April 2013

The energy-coupling factor (ECF) transporters constitute a novel family of conserved membrane transporters in prokaryotes that have a similar domain organization to the ATP-binding cassette transporters1, 2, 3. Each ECF transporter comprises a pair of cytosolic ATPases (the A and A′ components, or EcfA and EcfA′), a membrane-embedded substrate-binding protein (the S component, or EcfS) and a transmembrane energy-coupling component (the T component, or EcfT) that links the EcfA–EcfA′ subcomplex to EcfS. The structure and transport mechanism of the quaternary ECF transporter remain largely unknown. Here we report the crystal structure of a nucleotide-free ECF transporter from Lactobacillus brevis at a resolution of 3.5 Å. The T component has a horseshoe-shaped open architecture, with five α-helices as transmembrane segments and two cytoplasmic α-helices as coupling modules connecting to the A and A′ components. Strikingly, the S component, thought to be specific for hydroxymethyl pyrimidine, lies horizontally along the lipid membrane and is bound exclusively by the five transmembrane segments and the two cytoplasmic helices of the T component. These structural features suggest a plausible working model for the transport cycle of the ECF transporters.