The ribosomally synthesized and post-translationally modified peptide (RiPP), pyrroloquinoline quinone (PQQ), is a dehydrogenase cofactor synthesized by, but not exclusively used by, certain prokaryotes. RiPPs represent a rapidly expanding and diverse class of natural products—many of which have therapeutic potential—and the biosynthetic pathways for these are gaining attention. Five gene products from the pqq operon (PqqA, PqqB, PqqC, PqqD, and PqqE) are essential for PQQ biosynthesis. The substrate is the peptide PqqA, which is presented to the radical SAM enzyme PqqE by the small protein PqqD. PqqA is unstructured in solution, and only binds to PqqE when in complex with PqqD. PqqD is a member of a growing family of RiPP chaperone proteins (or domains in most cases) that present their associated peptide substrates to the initial RiPP biosynthesis enzymes. An X-ray crystal structure exists for dimeric Xanthomonas campestris PqqD (PDB ID: 3G2B), but PqqD is now known to act as a monomer under physiological conditions. In this study, the PqqD truncation from naturally fused Methylobacterium extorquens (Mex) PqqCD was overexpressed in Escherichia coli and MexPqqA was chemically synthesized. Solution NMR 1H-,15N-HSQC chemical shift studies have identified the PqqD residues involved in binding PqqA, and 1H, 13C, and 15N peak assignments for PqqD alone and for PqqD bound to PqqA are reported herein.
Bibliographical noteFunding Information:
Financial support for this work came from the National Institutes of Health grants GM-066569 (CMW) and GM-039296 (JPK). Special thanks to the Minnesota NMR Center for both professional expertise and access to spectrometers, and to the Minnesota Supercomputing Institute for their assistance in installing and configuring the annealing software to run on the supercomputer, Mesabi (reducing 20 h anneals to 30 min).
© 2016, Springer Science+Business Media Dordrecht.
- NMR resonance assignments
- Pyrroloquinoline quinone biosynthesis