Regulated methionine oxidation by monooxygenases

Abstract

Protein function can be regulated via post-translational modifications by numerous enzymatic and non-enzymatic mechanisms, including oxidation of cysteine and methionine residues. Redox-dependent regulatory mechanisms have been identified for nearly every cellular process, but the major paradigm has been that cellular components are oxidized (damaged) by reactive oxygen species (ROS) in a relatively unspecific way, and then reduced (repaired) by designated reductases. While this scheme may work with cysteine, it cannot be ascribed to other residues, such as methionine, whose reaction with ROS is too slow to be biologically relevant. However, methionine is clearly oxidized in vivo and enzymes for its stereoselective reduction are present in all three domains of life. Here, we revisit the chemistry and biology of methionine oxidation, with emphasis on its generation by enzymes from the monooxygenase family. Particular attention is placed on MICALs, a recently discovered family of proteins that harbor an unusual flavin-monooxygenase domain with an NADPH-dependent methionine sulfoxidase activity. Based on the structural and kinetic information we provide a rational framework to explain MICAL mechanism, inhibition, and regulation. Methionine residues that are targeted by MICALs are reduced back by methionine sulfoxide reductases, suggesting that reversible methionine oxidation may be a general mechanism analogous to the regulation by phosphorylation by kinases/phosphatases. The identification of new enzymes that catalyze the oxidation of methionine will open a new area of research at the forefront of redox signaling.

Amplification of F-Actin Disassembly and Cellular Repulsion by Growth Factor Signaling

“…The MICALs use their redox domain to exert their effects in multiple cell types (Manta and Gladyshev, 2017; Wilson, et al, 2016), but less is known of how this redox activity is regulated. Interestingly, MICALs have conserved proline (P)-rich PxxP motifs within their proline-rich region (Figures 1A and S1A), which are protein interaction modules known to serve as ligands for SH3 domains and regulate the biochemical function of different proteins.…”

“…The MICALs also play essential cellular roles through their ability to control actin organization in multiple cell types (Manta and Gladyshev, 2017; Wilson, et al, 2016), including within developing Drosophila bristle cells (Hung, et al, 2010), which have long provided a simple high-resolution single cell model for characterizing actin dependent events in vivo (Figure 1D; (Hung and Terman, 2011)). We therefore employed the bristle cell to determine if Abl is involved in Mical-mediated actin alterations.…”

“…( A ) Intramolecular interaction between Mical’s N-terminal and C-termini keeps Mical inactive (Manta and Gladyshev, 2017; Wilson, et al, 2016). Abl is also kept inactive through intramolecular interactions between Abl’s SH3 domain and an internal PxxP motif (Wang, 2014; Nagar, et al, 2003).…”

“…Recently, our approaches uncovered a direct pathway from the cell surface repulsive Semaphorin receptor Plexin (Plex) to the actin cytoskeleton – identifying an oxidation-reduction (redox) enzyme, Mical, that directly associates with both Plex and actin filaments, and induces F-actin disassembly via the posttranslational oxidation of actin (Hung, et al, 2011; Hung, et al, 2010; Terman, et al, 2002). The MICALs are now becoming widely recognized as using this F-actin disassembly Redox activity to alter the behaviors of multiple cell types (reviewed in (Manta and Gladyshev, 2017; Wilson, et al, 2016)) but little is known if other signal transduction pathways may intersect with Mical to direct actin cytoskeletal disassembly.…”

Methionine in proteins: The Cinderella of the proteinogenic amino acids

“…These redox reactions can be enzyme‐catalyzed. Thus, Met forms MetO by adding oxygen to its sulfur atom in a reaction that can be catalyzed at least by two different enzymes: methionine sulfoxide reductase A (MsrA, a bifunctional enzyme) that, when operating in the oxidizing direction, yields the S epimer of methionine sulfoxide (MetSO); and Mical, an enzyme that also exhibits stereospecificity, but, in this case, catalyzing the formation of the R epimer (MetRO) . The reduction back to methionine of these MetO epimers is mediated by MsrA and MsrB, respectively.…”