PqqD is a novel peptide chaperone that forms a ternary complex with the radical S-adenosylmethionine protein PqqE in the pyrroloquinoline quinone biosynthetic pathway. [Protein Structure and Folding]

March 27th, 2015 by Latham, J. A., Iavarone, A. T., Barr, I., Juthani, P. V., Klinman, J. P.

Pyrroloquinoline quinone (PQQ) is a product of a ribosomally-synthesized and post-translationally modified pathway consisting of five conserved genes, pqqA-E. PqqE is a radical S-adenosylmethionine (RS) protein with a C-terminal SPASM domain, and is proposed to catalyze the formation of a carbon-carbon bond between the glutamate and tyrosine side chains of the peptide substrate PqqA. PqqD is a 10 kDa protein with an unknown function, but is essential for PQQ production. Recently, in Klebsiella pneumoniae (Kp), PqqD and PqqE were shown to interact; however the stoichiometry and KD were not obtained. Here, we show that the PqqE and PqqD interaction transcends species, also occurring in Methylobacterium extorquens AM1 (Me). The stoichiometry of the MePqqD and MePqqE interaction is 1:1 and the KD, determined by surface plasmon resonance spectroscopy (SPR), was found to be ~ 12 μM. Moreover, using SPR and isothermal calorimetry techniques, we establish for the first time that MePqqD binds MePqqA tightly (KD ~ 200 nM). The formation of a ternary MePqqA-D-E complex was captured by native mass spectrometry and the KD for the MePqqAD-MePqqE interaction was found to be ~ 5 μM. Finally, using a bioinformatic analysis, we show that PqqD orthologues associate with RS-SPASM proteins found in peptide modification pathways. In conclusion, we propose that PqqD is a novel peptide chaperone and that PqqD orthologues may play a similar role in peptide modification pathways that use an RS-SPASM protein.
  • Posted in Journal of Biological Chemistry, Publications
  • Comments Off on PqqD is a novel peptide chaperone that forms a ternary complex with the radical S-adenosylmethionine protein PqqE in the pyrroloquinoline quinone biosynthetic pathway. [Protein Structure and Folding]