Structures of the Neisseria meningitides methionine-binding protein MetQ in substrate-free form and bound to l - and d -methionine isomers

Journal Article · 09 August 2019 · Protein Science

DOI: https://doi.org/10.1002/pro.3694 · OSTI ID:1623587

Nguyen, Phong T. ^[1]; Lai, Jeffrey Y. ^[2]; Kaiser, Jens T. ^[2]; Rees, Douglas C.  ^[2]

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1. California Institute of Technology (CalTech), Pasadena, CA (United States). Division of Chemistry and Chemical Engineering
2. California Institute of Technology (CalTech), Pasadena, CA (United States). Division of Chemistry and Chemical Engineering; California Institute of Technology (CalTech), Pasadena, CA (United States). Division of Chemistry and Chemical Engineering. Howard Hughes Medical Inst.

The bacterial periplasmic methionine-binding protein MetQ is involved in the import of methionine by the cognate MetNI methionine ATP binding cassette (ABC) transporter. The MetNIQ system is one of the few members of the ABC importer family that has been structurally characterized in multiple conformational states. Critical missing elements in the structural analysis of MetNIQ are the structure of the substrate-free form of MetQ, and detailing how MetQ binds multiple methionine derivatives, including both l- and d-methionine isomers. In this study, we report the structures of the Neisseria meningitides MetQ in substrate-free form and in complexes with l-methionine and with d-methionine, along with the associated binding constants determined by isothermal titration calorimetry. Structures of the substrate-free (N238A) and substrate-bound N. meningitides MetQ are related by a “Venus-fly trap” hinge-type movement of the two domains accompanying methionine binding and dissociation. l- and d-methionine bind to the same site on MetQ, and this study emphasizes the important role of asparagine 238 in ligand binding and affinity. A thermodynamic analysis demonstrates that ligand-free MetQ associates with the ATP-bound form of MetNI ~40 times more tightly than does liganded MetQ, consistent with the necessity of dissociating methionine from MetQ for transport to occur.

• Research Organization: SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: AC02-76SF00515
• OSTI ID: 1623587
• Journal Information: Protein Science, Vol. 28, Issue 10; ISSN 0961-8368
• Publisher: The Protein SocietyCopyright Statement
• Country of Publication: United States
• Language: English