Cinnamate:Coenzyme A Ligase from the Filamentous Bacterium Streptomyces coelicolor A3(2)
AUTOR(ES)
Kaneko, Masafumi
FONTE
American Society for Microbiology
RESUMO
4-Coumarate:coenzyme A ligase (4CL) plays a key role in phenylpropanoid metabolism, providing precursors for a large variety of important plant secondary metabolites, such as lignin, flavonoids, and phytoalexins. Although 4CLs have been believed to be specific to plants, a gene encoding a 4CL-like enzyme which shows more than 40% identity in amino acid sequence to plant 4CLs was found in the genome of the gram-positive, filamentous bacterium Streptomyces coelicolor A3(2). The recombinant enzyme, produced in Escherichia coli with a histidine tag at its N-terminal end, showed distinct 4CL activity. The optimum pH and temperature of the reaction were pH 8.0 and 30°C, respectively. The Km value for 4-coumarate and kcat were determined as 131 ± 4 μM and 0.202 ± 0.007 s−1, respectively. The Km value was comparable to those of plant 4CLs. The substrate specificity of this enzyme was, however, distinctly different from those of plant 4CLs. The enzyme efficiently converted cinnamate (Km, 190 ± 2 μM; kcat, 0.475 ± 0.012 s−1), which is a very poor substrate for plant 4CLs. Furthermore, the enzyme showed only low activity toward caffeate and no activity toward ferulate, both of which are generally good substrates for plant 4CLs. The enzyme was therefore named ScCCL for S. coelicolor A3(2) cinnamate CoA ligase. To determine the amino acid residues providing the unique substrate specificity of ScCCL, eight ScCCL mutant enzymes having a mutation(s) at amino acid residues that probably line up along the substrate-binding pocket were generated. Mutant A294G used caffeate as a substrate more efficiently than ScCCL, and mutant A294G/A318G used ferulate, which ScCCL could not use as a substrate, suggesting that Ala294 and Ala318 are involved in substrate recognition. Furthermore, the catalytic activities of A294G and A294G/A318G toward cinnamate and 4-coumarate were greatly enhanced compared with those of the wild-type enzyme.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=141888Documentos Relacionados
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