Adenosine triphosphate phosphoribosyl transferase (ATP-PRT) is involved in the first committed step of histidine biosynthetic pathway. The enzyme is allosterically inhibited by histidine, as a means of controlling the pathway in response to metabolic demant for histidine. Previously, two molecular architectures including the homo-hexameric long form and hetero-octameric short form have been described for ATP-PRT.1 Recently, a third structure the “super-long” form has been revealed by our examination of protein sequences. This super-long form is homo-tetrameric, resembling the non-covalent hetero-octameric complex of the short form, and has been studied from Leuconostoc mesenteroides (denoted LmeHisZGFusion). It appears likely that this protein has evolved via the fusion of genes encoding the short form complex and undergoes a large conformational change upon histidine binding.
We are currently in the process of characterisation of this enzyme and solving the X-ray crystal structure. The investigation on the evolution is pursued using molecular biology techniques. Studies are being conducted to assess whether the fission of LmeHisZGFusion into its constituents HisZ and HisGs subunits, leads to a functional non-covalent complex which resembles the short form ATP-PRTase.2 We were able to construct the truncated HisZ subunit and are in the process of exploring its characteristics. Additionally, genetic knockout complementation studies are being employed to assess the essentiality of this gene product to the survival of the strain.