title: Structural Characterization of Heme Environmental Mutants of CgHmuT that Shuttles Heme Molecules to Heme Transporters.
abstract: Corynebacteria contain a heme uptake system encoded in hmuTUV genes, in which HmuT protein acts as a heme binding protein to transport heme to the cognate transporter HmuUV. The crystal structure of HmuT from Corynebacterium glutamicum (CgHmuT) reveals that heme is accommodated in the central cleft with His141 and Tyr240 as the axial ligands and that Tyr240 forms a hydrogen bond with Arg242. In this work, the crystal structures of H141A, Y240A, and R242A mutants were determined to understand the role of these residues for the heme binding of CgHmuT. Overall and heme environmental structures of these mutants were similar to those of the wild type, suggesting that there is little conformational change in the heme-binding cleft during heme transport reaction with binding and the dissociation of heme. A loss of one axial ligand or the hydrogen bonding interaction with Tyr240 resulted in an increase in the redox potential of the heme for CgHmuT to be reduced by dithionite, though the wild type was not reduced under physiological conditions. These results suggest that the heme environmental structure stabilizes the ferric heme binding in CgHmuT, which will be responsible for efficient heme uptake under aerobic conditions where Corynebacteria grow.
authors.affiliation: Institute for Molecular Science, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki 444-8787, Japan. nmuraki@ims.ac.jp.|Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki 444-8787, Japan. nmuraki@ims.ac.jp.
authors.forename: Norifumi
authors.initials: N
authors.lastname: Muraki
authors.affiliation: Institute for Molecular Science, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki 444-8787, Japan. bb20114202@cc.nagasaki-u.ac.jp.|Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki 444-8787, Japan. bb20114202@cc.nagasaki-u.ac.jp.
authors.forename: Chihiro
authors.initials: C
authors.lastname: Kitatsuji
authors.affiliation: Graduate School of Chemical Sciences and Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan. m6_ed4_science@ec.hokudai.ac.jp.|Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan. m6_ed4_science@ec.hokudai.ac.jp.
authors.forename: Mariko
authors.initials: M
authors.lastname: Ogura
authors.affiliation: Graduate School of Chemical Sciences and Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan. uchida@sci.hokudai.ac.jp.|Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan. uchida@sci.hokudai.ac.jp.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Uchida
authors.affiliation: Graduate School of Chemical Sciences and Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan. koichiro@sci.hokudai.ac.jp.|Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan. koichiro@sci.hokudai.ac.jp.
authors.forename: Koichiro
authors.initials: K
authors.lastname: Ishimori
authors.affiliation: Institute for Molecular Science, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki 444-8787, Japan. aono@ims.ac.jp.|Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki 444-8787, Japan. aono@ims.ac.jp.|Department of Structural Molecular Science, SOKENDAI, The Graduate University for Advanced Studies, 5-1 Higashiyama, Myodaiji, Okazaki 444-8787, Japan. aono@ims.ac.jp.
authors.forename: Shigetoshi
authors.initials: S
authors.lastname: Aono
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D048230:Corynebacterium glutamicum / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D018360:Crystallography, X-Ray; D006418:Heme / Q000378:metabolism*; D000081062:Heme-Binding Proteins; D006420:Hemeproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D009154:Mutation; D011485:Protein Binding; D017433:Protein Structure, Secondary
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D000081062:Heme-Binding Proteins; D006420:Hemeproteins; D006418:Heme
keywords: X-ray crystallography; heme transport; heme uptake; substrate binding protein in ATP-binding cassette (ABC) transporter