title: Ammonia channel couples glutaminase with transamidase reactions in GatCAB.
abstract: The formation of glutaminyl transfer RNA (Gln-tRNA(Gln)) differs among the three domains of life. Most bacteria employ an indirect pathway to produce Gln-tRNA(Gln) by a heterotrimeric glutamine amidotransferase CAB (GatCAB) that acts on the misacylated Glu-tRNA(Gln). Here, we describe a series of crystal structures of intact GatCAB from Staphylococcus aureus in the apo form and in the complexes with glutamine, asparagine, Mn2+, and adenosine triphosphate analog. Two identified catalytic centers for the glutaminase and transamidase reactions are markedly distant but connected by a hydrophilic ammonia channel 30 A in length. Further, we show that the first U-A base pair in the acceptor stem and the D loop of tRNA(Gln) serve as identity elements essential for discrimination by GatCAB and propose a complete model for the overall concerted reactions to synthesize Gln-tRNA(Gln).
authors.affiliation: Faculty of Advanced Life Sciences, Hokkaido University, Sapporo 060-0810, Japan.
authors.forename: Akiyoshi
authors.initials: A
authors.lastname: Nakamura
authors.forename: Min
authors.initials: M
authors.lastname: Yao
authors.forename: Sarin
authors.initials: S
authors.lastname: Chimnaronk
authors.forename: Naoki
authors.initials: N
authors.lastname: Sakai
authors.forename: Isao
authors.initials: I
authors.lastname: Tanaka
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D019881:Aminoacyltransferases / Q000378:metabolism; D000641:Ammonia / Q000378:metabolism*; D001051:Apoenzymes / Q000737:chemistry / Q000378:metabolism; D001216:Asparagine / Q000378:metabolism; D020029:Base Pairing; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D005972:Glutaminase / Q000378:metabolism; D005973:Glutamine / Q000737:chemistry* / Q000378:metabolism; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D008274:Magnesium / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D012329:RNA, Bacterial / Q000737:chemistry / Q000378:metabolism; D012346:RNA, Transfer, Amino Acyl / Q000737:chemistry / Q000378:metabolism*; D012351:RNA, Transfer, Gln / Q000737:chemistry* / Q000378:metabolism; D013211:Staphylococcus aureus / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
chemical_list: D001051:Apoenzymes; D021122:Protein Subunits; D012329:RNA, Bacterial; D012346:RNA, Transfer, Amino Acyl; D012351:RNA, Transfer, Gln; D005973:Glutamine; D008345:Manganese; D000244:Adenosine Diphosphate; D001216:Asparagine; D000641:Ammonia; D019881:Aminoacyltransferases; C023175:transamidases; D005972:Glutaminase; D008274:Magnesium