P5: Domain alternation strategy by the ANL superfamily of adenylating enzymes: Mechanism of a 4-coumarate:CoA ligase

The ANL superfamily of adenylating enzymes contains three subfamilies: acyl- and aryl-CoA synthetases, the adenylating domains of non-ribosomal peptide synthetases, and luciferases. These enzymes catalyze a two-step reaction, sharing a conserved adenylation partial reaction in the first step. They share 20% sequence identity and have highly similar structure. Members of this superfamily use a remarkable domain alternation strategy to catalyze the two partial reactions. 4-coumarate:CoA ligase (4CL; EC 6.2.1.12) belongs to the acyl- and aryl-CoA synthetase subfamily. 4CL is a central enzyme in the phenylpropanoid pathway in plants, which provides the precursors for numerous important metabolites. For its important role in regulating the carbon flow in plants, the engineering of 4CL has attracted extensive interests. Here we show a series of crystal structures of a 4CL enzyme, which showcases the domain alternation strategy employed by the ANL superfamily, sheds light on the catalytic mechanism of 4CL enzymes, and provides insights into their substrate specificity.