1-Aminocyclopropane-1-carboxylate (ACC) deaminase-mediated reduction of ethylene generation in plants under abiotic stresses is a key mechanism by which bacteria can promote plant growth. Misidentification of ACC deaminase and the ACC deaminase structure gene (acdS) can lead to overestimation of the number of bacteria containing ACC deaminase and their function in ecosystems. Previous non-specific amplification of acdS homologs has led to an overestimation of the horizontal transfer of acdS genes. Here, we designed consensus-degenerate hybrid oligonucleotide primers (acdSf3, acdSr3 and acdSr4) based on differentiating the key residues in ACC deaminases from those of homologs for specific amplification of partial acdS genes. PCR amplification, sequencing and phylogenetic analysis identified acdS genes from a wide range of proteobacteria and actinobacteria. PCR amplification and a genomic search did not find the acdS gene in bacteria belonging to Pseudomonas stutzeri or in the genera Enterobacter, Klebsiella or Bacillus. We showed that differentiating the acdS gene and ACC deaminase from their homologs was crucial for the molecular identification of bacteria containing ACC deaminase and for understanding the evolution of the acdS gene. We provide an effective method for screening and identifying bacteria containing ACC deaminase.
Uridine diphosphate-glucuronosyltransferases (UGTs) are the most important phase II enzymes in human drug metabolism. Using permeabilized recombinant fission yeast cells (enzyme bags), we demonstrate that UGT1A5 can catalyze an N-glucuronidation reaction. We characterized two new polymorphic UGT1A5 variants: a common ninefold mutant (UGT1A5*8) with double-fold activity and a much rarer sixfold mutant (UGT1A5*9), which has the same activity as the wild-type. Molecular modeling studies indicate that the minor effects of all mutations, except for Gly259Arg, are due to their distance to the substrate binding site. Extensive molecular dynamics simulations revealed that the Gly259Arg mutation stabilizes helix Q through a newly formed hydrogen bonding network, which places the cofactor in a much more favorable geometry in UGT1A5*8 as compared to the wild-type.
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