Pyrroloquinoline Quinone (PQQ) Biosynthesis

PQQ is an important redox-active cofactor used by a number of bacterial dehydrogenases. PQQ is also important for human health and its role as a vitamin in mammals has recently been suggested. Although much is known about the function of enzymes that use PQQ as a cofactor, relatively little is known about the chemical steps and therefore the function of the enzymes involved in PQQ biosynthesis. Six gene products (PqqA-F) are required to derive PQQ from glutamate and tyrosine residues encoded in the precursor peptide PqqA. In previous work we successfully characterized the last step of PQQ biosynthesis and discovered that PqqC (EC 1.3.3.11) is a novel cofactor-less oxygenase (PNAS 2004; JACS 2004; Proteins 2004). In this project we want to continue our functional and structural studies on PqqC and focus on mechanistic details of the oxidation reaction. In addition, we plan to extend our work on the remaining PQQ biosynthesis proteins and study their reactions using biophysical methods combined with mutagenesis of critical residues. We have already established proof of concept with obtaining the structure of PqqB and active protein for PqqE and PqqF. The overall objective of this proposal is to understand the biosynthesis pathway for pyrroloquinoline quinone (PQQ) formation.