Structural and biophysical analysis of a Haemophilus influenzae tripartite ATP-independent periplasmic (TRAP) transporter

• DOI: 10.7554/elife.92307
• Publication Date: 2023-10-30T15:41:57Z
• Authors: Michael J Currie; James S Davies; Mariafrancesca Sc...; Ashutosh Gulati; Joshua D Wright; Michael C Newton-...; Gayan S Abeysekera; Ramaswamy Subrama...; Weixiao Y Wahlgren; Rosmarie Friemann; Jane R Allison; Peter D Mace; Michael DW Griffin; Borries Demeler; Soichi Wakatsuki; David Drew; Cesare Indiveri; Renwick CJ Dobson; Rachel A North
• Keywords: Trap (plumbing); Structural Biology

Tripartite ATP-independent periplasmic (TRAP) transporters are secondary-active that receive their substrates via a soluble-binding protein to move bioorganic acids across bacterial or archaeal cell membranes. Recent cryo-electron microscopy (cryo-EM) structures of TRAP provide broad framework understand how they work, but the mechanistic details transport not yet defined. Here we report cryo-EM structure Haemophilus influenzae N-acetylneuraminate transporter (HiSiaQM) at 2.99 Å resolution (extending 2.2 core), revealing new features. The improved (the previous HiSiaQM is 4.7 resolution) permits accurate assignment two Na+ sites and architecture substrate-binding site, consistent with mutagenic functional data. Moreover, rather than monomer, homodimer. We observe lipids dimer interface, as well lipid trapped within fusion links SiaQ SiaM subunits. show affinity (KD) for complex between soluble HiSiaP in micromolar range related SiaP can bind HiSiaQM. This work provides key data enhances our understanding 'elevator-with-an-operator' mechanism transporters.