title: Molecular evolution of hisB genes.
abstract: The sixth and eighth steps of histidine biosynthesis are catalyzed by an imidazole glycerol-phosphate (IGP) dehydratase (EC 4.2.1.19) and by a histidinol-phosphate (HOL-P) phosphatase (EC 3.1.3.15), respectively. In the enterobacteria, in Campylobacter jejuni and in Xylella/Xanthomonas the two activities are associated with a single bifunctional polypeptide encoded by hisB. On the other hand, in Archaea, Eucarya, and most Bacteria the two activities are encoded by two separate genes. In this work we report a comparative analysis of the amino acid sequence of all the available HisB proteins, which allowed us to depict a likely evolutionary pathway leading to the present-day bifunctional hisB gene. According to the model that we propose, the bifunctional hisB gene is the result of a fusion event between two independent cistrons joined by domain-shuffling. The fusion event occurred recently in evolution, very likely in the proteobacterial lineage after the separation of the gamma- and the beta-subdivisions. Data obtained in this work established that a paralogous duplication event of an ancestral DDDD phosphatase encoding gene originated both the HOL-P phosphatase moiety of the E. coli hisB gene and the gmhB gene coding for a DDDD phosphatase, which is involved in the biosynthesis of a precursor of the inner core of the outer membrane lipopolysaccharides (LPS).
authors.affiliation: Dipartimento di Biologia Animale e Genetica, Via Romana 17-19, 1-50125, Firenze, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Brilli
authors.forename: Renato
authors.initials: R
authors.lastname: Fani
mesh_terms: D000595:Amino Acid Sequence; D001419:Bacteria / Q000235:genetics*; D016000:Cluster Analysis; D030541:Databases, Genetic; D019143:Evolution, Molecular; D020440:Gene Duplication; D006639:Histidine / Q000235:genetics*; D006836:Hydro-Lyases / Q000235:genetics; D008957:Models, Genetic; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D016415:Sequence Alignment
chemical_list: D012336:RNA, Ribosomal, 16S; D006639:Histidine; D006836:Hydro-Lyases; C021434:imidazoleglycerolphosphate dehydratase