Chemoselectivity in cytochrome c catalyzed carbene transfer into Si–H and N–H bonds

In a new study published in the Journal of the American Chemical Society, Dr. Marc Garcia-Borràs reports a joint computational and experimental study together with the groups of Prof. Frances Arnold (Caltech, USA) and Prof. Ken Houk (UCLA, USA) to characterize the mechanism and chemoselective formation of carbon–silicon bonds. This process occurs via carbene insertions into Si–H bonds and is catalyzed by a previously evolved cytochrome c carbene transferase from Rhodothermus marinus (Rma cyt c, Science2016, 354, 1048-1051).

Using multiscale computational approaches combined with experimental characterizations, it was determined how this enzyme-catalyzed reaction works. The authors discovered that mutations introduced by directed evolution impact mainly the control of conformational dynamics of a protein loop that covers the substrate access to the iron-carbene active species. Using extensive molecular dynamics (MD) simulations it was found that by modifying the loop conformational dynamics, the enzymatic activity could be enhanced up to 7-fold. More importantly, this loop is responsible for the chemoselectivity control acquired by the enzyme during evolution, by controlling how the substrate approaches the iron-carbene intermediate.

Taking advantage of the new mechanistic insights, the loop conformational dynamics was further manipulated to switch the enzyme chemoselectivity from silylation to amination (from >97% silylation in the Rma TDE variant to >90% amination in a new Rma TDFPI variant) using a substrate containing both N?H and Si?H functionalities.

This study demonstrates that information on protein structure and conformational dynamics, combined with knowledge of mechanism, leads to understanding of how non-natural and selective chemical transformations can be introduced into the biological world, and provides better understanding of how abiological carbene transferases control chemoselectivity.

The Research Team headed by Dr. Garcia-Borràs is currently applying these computational approaches to investigate and characterize the formation of key enzymatic intermediates, with the final aim to design new enzymes that catalyze new-to-nature reactions interesting from a synthetic perspective.

The paper has recently been published in the Journal of the American Chemical Society:

M. Garcia-Borràs, S.B.J. Kan, R.D. Lewis, A. Tang, G. Jimenez-Osés, F.H. Arnold, and K.N. Houk
“Origin and Control of Chemoselectivity in Cytochromec Catalyzed Carbene Transfer into Si–H and N–H bonds”
J. Am. Chem. Soc. 2021, online, ASAP
DOI: 10.1021/jacs.1c02146

Girona, May 4, 2021
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