The Lonely Guy (LOG) Homologue SiRe_0427 from the Thermophilic Archaeon Sulfolobus islandicus REY15A Is a Phosphoribohydrolase Representing a Novel Group

Lonely Guy (LOG) is an essential enzyme for the final biosynthesis of cytokinins, which regulate almost every aspect of growth and development in plants. LOG protein was originally discovered 12 years ago in a strain ofOryza sativa with a distinct floral phenotype of a single stamen. Recently, the presence of LOG homologues has been reported inMycobacterium tuberculosis , an obligate human pathogen. To date, active LOG proteins have been reported in plants, pathogenic and nonpathogenic fungi, and bacteria, but there have been no experimental reports of LOG protein from archaea. In the current work, we report the identification of a LOG homologue active on AMP fromSulfolobus islandicus REY15A, a thermophilic archaeon. The protein likely forms a tetramer in solution and represents a novel evolutionary lineage. The results presented here expand our knowledge regarding proteins with phosphoribohydrolase activities and open an avenue for studying signal transduction networks of archaea and potential applications of LOG enzymes in agriculture and industry.