Bifunctional His(IE) enzymes from E. coli and S. typhimurium act as dimers (Winkler, 1996). The crystal IFN-beta Protein medchemexpress structure of phosphoribosyl-ATP pyrophosphatase from M. tuberculosis (HisEMt) was solved and revealed that additionally, it types a dimer (Javid-Majd et al., 2008). The amino acid sequences of HisECg and HisEMt share 62 identity and 90 similarity, assuming a very similar structure for both proteins. Depending on this deduced 3D structure, native HisECg probably acts as a dimer, as well. 5 ProFAR isomerase (HisA) The fourth step of histidine biosynthesis is performed by 5ProFAR isomerase. This enzyme catalyses an internal redox reaction converting 5ProFAR to 5-[(5phospho-1-deoxyribulos-1-ylamino)methylideneamino]-1(5-phosphoribosyl)imidazole-4-carboxamide (PRFAR) (Alifano et al., 1996). The native enzymes from E. coli and S. typhimurium act as monomers (Winkler, 1996). The crystal structure of 5ProFAR isomerase from M. tuberculosis (PriAMt) encoded by the priA gene was solved lately (Due et al., 2011). Interestingly, PriAMt is also involved in tryptophan biosynthesis because of its phosphoribosylanthranilate isomerase activity. So far it cannot be excluded that 5ProFAR isomerase from C. glutamicum (HisACg) can also be involved in tryptophan biosynthesis. Nonetheless, deletion of hisA resulted in histidine auxotrophy only (R.K. Kulis-Horn, unpubl. obs.), indicating that C. glutamicum must at the very least possess a single further gene coding to get a phosphoribosylanthranilate isomerase. This enzyme activity is probably exerted by the trp(CF) gene item, already annotated as a bifunctional phosphoribosylanthranilate isomerase/indoleglycerolphosphate synthase in C. glutamicum (Kalinowski et al., 2003). Nonetheless, the 3D structure on the bifunctional PriAMt enzyme, exhibiting 61 identity and 89 similarity on amino acid level, enables a deeper insight in to the structure of 5ProFAR isomerase from C. glutamicum (HisACg). Depending on these data, native HisACg probably acts as a monomer with an (a/b)eight barrel fold. [Corrections added on 09 October 2013, soon after very first on the internet publication: In the paragraph above, occurrences on the gene name “pirA” are now amended to “priA”.]?2013 The Authors. Microbial Biotechnology published by John Wiley Sons Ltd and Arginase-1/ARG1, Human (N-His) Society for Applied Microbiology, Microbial Biotechnology, 7, 5?10 R. K. Kulis-Horn, M. Persicke and J. Kalinowski Imidazoleglycerol-phosphate synthase (HisFH) The fifth step of histidine biosynthesis would be the conversion of PRFAR to the subsequent histidine intermediate imidazole-glycerol phosphate (IGP) and also the byproduct 1-(5-phosphoribosyl)-5-amino-4-imidazolecarboxamide (AICAR), an intermediate of de novo purine biosynthesis (Alifano et al., 1996). Glutamine is utilized as nitrogen donor within this amination step releasing glutamate (Smith and Ames, 1964). Mutations in either hisH or hisF outcome in histidine auxotrophy of S. typhimurium (Hartman et al., 1960). These genes had been later linked towards the fifth step of histidine biosynthesis, despite the fact that each were initially assumed to code for independent enzymes catalysing diverse steps in the conversion of PRFAR to IGP and AICAR (Smith and Ames, 1964). The exact role of hisF and hisH gene goods remained elusive for a lot of years. It was finally demonstrated for hisF and hisH of E. coli that the two gene products act as a stable 1:1 dimeric complex which constitutes the IGP synthase holoenzyme (Klem and Davisson, 1993). Corynebacterium glutamicum also possesses hisF and hisH genes. They exhibi.