Characterization of the ABC methionine transporter from Neisseria meningitidis reveals that lipidated MetQ is required for interaction

NmMetQ is a substrate-binding protein (SBP) from Neisseria meningitidis that has been identified as a surface-exposed candidate antigen for meningococcal vaccines. However, this location for NmMetQ challenges the prevailing view that SBPs in Gram-negative bacteria are localized to the periplasmic space to promote interaction with their cognate ABC transporter embedded in the bacterial inner membrane. To elucidate the roles of NmMetQ, we characterized NmMetQ with and without its cognate ABC transporter (NmMetNI). Here, we show that NmMetQ is a lipoprotein (lipo-NmMetQ) that binds multiple methionine analogs and stimulates the ATPase activity of NmMetNI. Using single-particle electron cryo-microscopy, we determined the structures of NmMetNI in the presence and absence of lipo-NmMetQ. Based on our data, we propose that NmMetQ tethers to membranes via a lipid anchor and has dual function and localization, playing a role in NmMetNI-mediated transport at the inner membrane and moonlighting on the bacterial surface. ; © 2021, Sharaf et al. This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited. Received: 24 April 2021; Preprinted: 04 May 2021; Accepted: 18 August 2021; Published: 19 August 2021. We thank Jacob Parres-Gold and Dr. Sara J Weaver for useful discussions and Dr. Lilien Voong for critical reading of the manuscript. We also thank Dr. Songye Chen and Dr. Andrey Malyutin of the Beckman Institute Resource Center for Transmission Electron Microscopy at Caltech for assistance with data collection. This research utilized instrumentation made available by the Caltech CCE Multiuser Mass Spectrometry Laboratory, the CCE Liquids NMR Facility, and the Beckman Institute cryo-EM facility. NGS was supported by the Postdoctoral Enrichment Program from the Burroughs Wellcome Fund and DCR is a Howard Hughes Medical Institute Investigator. The funders had no role in study design, data ...