Structural Impact of Site-Specific Calmodulin Methionine Oxidation

Abstract

We have examined the structural consequences of methionine (Met) oxidation in the calcium-sensing muscle regulatory protein calmodulin (CaM) using molecular dynamics simulations. Protein oxidation by reactive oxygen species (ROS), and subsequent reduction by the antioxidant enzyme methionine sulfoxide reductase, has emerged as a crucial cell regulatory mechanism. In the context of oxidative stress, protein oxidation is implicated in disease progression and biological aging. Our goal is to bridge our understanding of muscle dysfunction and protein oxidation with atomic-level insights into site-specific methionine oxidation and calmodulin structural dynamics. We have carried out multiple 500 ns molecular dynamics simulations of explicitly solvated calmodulin, both the calcium-bound (1cll) and apo (1cfc) crystal structures. Results from preliminary simulations suggest that the structure of calcium bound CaM is structurally insensitive to methionine oxidation, while methionine oxidation in apo CaM causes considerable changes the relative orientation of the N-ter and C-ter lobes. Our work is a component of a larger study in which spectroscopic distance measurements and nuclear magnetic resonance experiments are being carried out for site-specifically oxidized CaM in both the calcium bound and apo biochemical states. We expect that our in silico results will bring atomic-level insight to spectroscopic measurements, and will be integral to creating a more complete model for oxidation-induced changes in calmodulin structural dynamics. Further, we anticipate that our results will be applicable to the many biological and pharmaceutical contexts in which a detailed understanding of protein oxidation, function and structure relationships is sought. This work is supported by an NIH grant to Dave Thomas (2R37AG026160-06) and the Minnesota Supercomputing Institute.