Kakali Sen, STFC Scientific Computing

Cytochromes P460 oxidise hydroxylamine within the nitrogen cycle and contain as their active site an unusual catalytic c-type haem where the porphyrin is crosslinked to the protein via a lysine residue in addition to the canonical cross links from cysteine residues. Understanding how enzymes oxidise hydroxylamine into either nitrous oxide or nitric oxide has implications for climate change.

Hybrid QM/MM calculations with ChemShell were combined with high resolution structures from synchrotron and XFEL sources paired with crystal spectroscopies to study in details the crosslink structure of catalytically active cytochrome P460s from methane oxidising Methylococcus capsulatus (Bath) bacteria (McP460). The QM/MM simulations helped identify the lowest energy structures and combining with TD-DFT at QM/MM level enabled the prediction of electronic absorption spectra providing a crucial validation to the experimental structures of McP460. We have shown that native McP460 possesses an unusual double crosslink between lysine and haem in its resting oxidised state and reverts to single crosslink structure on reduction.

Citation:

H. E. Pfalzgraf, A. G. Rao, K. Sen, H. R. Adams, M. Edwards, Y. Lu, C. Yong, S. Jaho, T. Tosha, H. Sugimoto, S. Horrell, J. Beilsten-Edmands, R. L. Owen, C. R. Andrew, J. A. R. Worrall, I. Tews, A. J. Mulholland, M. A. Hough and T. W. Keal (2025) “Double crossed? Structural and computational studies of an unusually crosslinked haem in Methylococcus capsulatus cytochrome P460”, Chem. Sci., 16, 16266-16283. DOI: 10.1039/d5sc04213e