Dehydroquinase (DHQase), type II. Dehydroquinase (or 3-dehydroquinate dehydratase) catalyzes the reversible dehydration of 3-dehydroquinate to form 3-dehydroshikimate. This reaction is part of two metabolic pathways: the biosynthetic shikimate pathway and the catabolic quinate pathway. There are two types of DHQases, which are distinct from each other in amino acid sequence and three-dimensional structure. Type I enzymes usually catalyze the biosynthetic reaction using a syn elimination mechanism. In contrast, type II enzymes, found in the quinate pathway of fungi and in the shikimate pathway of many bacteria, are dodecameric enzymes that employ an anti elimination reaction mechanism.
Comment:The active site resides at the interface between two QHQase monomers in a trimer. Residues from two monomers contribute to one active site. There are three active sites in a trimer and 12 in the DHQase dodecamer. Unfolding and refolding studies show that the trimer is the minimum catalytic unit of the enzyme.
Structure:2C57_ABC; Helicobacter pylori type II DHQase trimer binds three 2,3-anhydro-quinic acid molecules; defined at 3.5A contacts
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