The final two steps of the meta-cleavage pathway for catechol degradation in Pseudomonas sp. strain CF600 involve the conversion of 4-hydroxy-2-ketovalerate to pyruvate and acetyl coenzyme A by the enzymes 4-hydroxy-2-ketovalerate aldolase and NAD - dependent acylating aldehyde dehydrogenase, the products of the dmpG and dmpF genes.  Biochemical studies indicate that these two enzymes comprise a bifunctional heterodimer (DmpFG, molecular mass 71 kDa), and suggest that the product of the aldolase reaction is transferred to the dehydrogenase active site via a channeling mechanism.  The current structure of wild type DmpFG heterodimer (see figure) shows a tunnel between the two subunits which is the right size for substrate transfer.

In order to understand the precise mechanism of substrate channeling and the protein - protein interactions that mediate the channeling activity, we are pursuing further mutagenic and crystallographic studies of this bifunctional enzyme.