Structurally diverse dehydroshikimate dehydratase variants participate in microbial quinate catabolism

Quinate and shikimate can be degraded by a number of microbes. Dehydroshikimate dehydratases (DSDs) play a central role in this process, catalyzing the conversion of 3-dehydroshikimate to protocatechuate, a common intermediate of aromatic degradation pathways. DSDs have applications in metabolic engineering for the production of valuable protocatechuate-derived molecules. Although a number of Gram-negative bacteria are known to catabolize quinate and shikimate, only limited information exists on the quinate/shikimate catabolic enzymes found in these organisms. Here, we have functionally and structurally characterized a putative DSD designated QuiC1, which is present in some pseudomonads. The QuiC1 protein is not related by sequence with previously identified DSDs from the Gram-negative genus, Acinetobacter, but instead shows limited sequence identity in its N-terminal half with fungal DSDs. Analysis of a Pseudomonas aeruginosa quiC1 gene knock-out demonstrates that it is important for growth on either quinate or shikimate. The structure of a QuiC1 enzyme from P. putida reveals that the protein is a fusion of two distinct modules: an N-terminal sugar phosphate isomerase-like domain associated with DSD activity and a novel C-terminal hydroxyphenylpyruvate dioxygenase-like domain. The results of this study highlight the considerable diversity of enzymes that participate in quinate/shikimate catabolism in different microbes.