The interaction of ammonia and xenon with the imidazole glycerol phosphate synthase fromThermotoga maritimaas detected by NMR spectroscopy

摘要: The imidazole glycerol phosphate (ImGP) synthase from the hyperthermophilic bacterium Thermotoga maritima is a 1:1 complex of glutaminase subunit HisH and cyclase HisF. It has been proposed that ammonia generated by transported through channel to active site HisF, which generates intermediates histidine de novo biosynthesis 5-aminoimidazole-4-carboxamideribotide. Solution NMR spectroscopy ammonium chloride-titrated samples was used study interaction NH3 with amino acids inside this channel. Although numerous residues showed 15N chemical shift changes, most these changes were caused nonspecific ionic strength effects. However, several interactions appeared be specific. Remarkably, acid residue Thr 78—which located in central channel—shows large change upon titration chloride. This result reduced catalytic activity Thr78Met mutant indicate special role channeling. To detect further characterize internal cavities might for example contribute channeling, HisF noble gas xenon analyzed solution using 1H-15N HSQC experiments. results contains three distinct cavities, could identified xenon-induced neighboring residues. Two are at opposite ends substrate N′-[(5′-phosphoribulosyl)formimino]-5-aminoimidazole-4-carboxamide-ribonucleotide (PRFAR) binding groove. third cavity interior β-barrel overlaps putative transport