Molecular evolution of acetohydroxyacid synthase in bacteria.

Acetohydroxyacid synthase (AHAS) is the key enzyme in the biosynthetic pathways of branched chain amino acids in bacteria. Since it does not exist in animal and plant cells, AHAS is an attractive target for developing antimicrobials and herbicides. In some bacteria, there is a single copy of AHAS, while in others there are multiple copies. Therefore, it is necessary to investigate the origin and evolutionary pathway of various AHASs in bacteria. In this study, all the available protein sequences of AHAS in bacteria were investigated, and an evolutionary model of AHAS in bacteria is proposed, according to gene structure, organization and phylogeny. Multiple copies of AHAS in some bacteria might be evolved from the single copy of AHAS, the ancestor. Gene duplication, domain deletion and horizontal gene transfer might occur during the evolution of this enzyme. The results show the biological significance of AHAS, help to understand the functions of various AHASs in bacteria, and would be useful for developing industrial production strains of branched chain amino acids or novel antimicrobials.