Insights into the Dynamics and Dissociation Mechanism of a Protein Redox Complex Using Molecular Dynamics

J Chem Inf Model. 2017 Sep 25;57(9):2344-2350. doi: 10.1021/acs.jcim.7b00421. Epub 2017 Sep 12.

Abstract

Leishmania major peroxidase (LmP) is structurally and functionally similar to the well-studied yeast Cytochrome c peroxidase (CCP). A recent Brownian dynamics study showed that L. major Cytochrome c (LmCytc) associates with LmP by forming an initial complex with the N-terminal helix A of LmP, followed by a movement toward the electron transfer (ET) site observed in the LmP-LmCytc crystal structure. Critical to forming the active electron transfer complex is an intermolecular Arg-Asp ion pair at the center of the interface. If the dissociation reaction is effectively the reverse of the association reaction, then rupture of the Asp-Arg ion pair should be followed by movement of LmCytc back toward LmP helix A. To test this possibility, we have performed multiple molecular dynamics (MD) simulations of the LmP-LmCytc complex. In five separate simulations, LmCytc is observed to indeed move toward helix A, and in two of the simulations, the Asp-Arg ion pair breaks, which frees LmCytc to fully associate with the LmP helix A secondary binding site. These results support the "bind and crawl" or "velcro" mechanism of association, wherein LmCytc forms a nonspecific electrostatic complex with LmP helix A, followed by a "crawl" toward the ET-active site, where the Asp-Arg ion pair holds the LmCytc in position for rapid ET. These simulations also point to Tyr134LmP as being important in the association/dissociation reactions. Experimentally mutating Tyr134 to Phe was found to decrease Km by 3.6-fold, which is consistent with its predicted role in complex formation by MD simulations.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Cytochrome-c Peroxidase / chemistry*
  • Cytochrome-c Peroxidase / metabolism*
  • Heme / metabolism
  • Leishmania major / enzymology*
  • Molecular Dynamics Simulation*
  • Mutation
  • Oxidation-Reduction
  • Peroxidase / chemistry*
  • Peroxidase / genetics
  • Peroxidase / metabolism*
  • Protein Conformation

Substances

  • Heme
  • Cytochrome-c Peroxidase
  • Peroxidase