title: Oxidation and phosphorylation of MAP kinase 4 cause protein aggregation.
abstract: Mitogen-activated protein kinase (MPK) cascades are highly conserved signaling pathways that respond to environmental cues. Arabidopsis MPK4 has been identified as a stress-responsive protein kinase. Here we demonstrate that Brassica napus MPK4 (BnMPK4) is activated by hydrogen peroxide (H2O2) and phytohormone abscisic acid (ABA). Transient expression of a constitutively active BnMPK4 causes H2O2 production and cell death in Nicotiana benthamiana leaves. However, little is known about how H2O2 contributes to the regulation of MPK4 kinase function. Biochemical analysis revealed that recombinant BnMPK4 autophosphorylates on both threonine and tyrosine residues in the activation loop. In the presence of H2O2, phosphorylation of BnMPK4 caused protein aggregation in vitro. The aggregation of BnMPK4 could be reversed to the monomeric form by reducing reagents. Point-mutation of cysteine codons indicated that cysteine 232 is involved in protein aggregation. Our results suggest that BnMPK4 is involved in reactive oxygen species (ROS) signaling and metabolism, and its aggregation may be modulated by redox.
authors.affiliation: Department of Biology, University of Florida, Gainesville, FL 32610, USA; Genetics Institute, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Tong
authors.initials: T
authors.lastname: Zhang
authors.affiliation: Department of Biology, University of Florida, Gainesville, FL 32610, USA; Genetics Institute, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Mengmeng
authors.initials: M
authors.lastname: Zhu
authors.affiliation: Department of Plant Pathology, University of Florida, Gainesville, FL 32610, USA; Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Wen-yuan
authors.initials: WY
authors.lastname: Song
authors.affiliation: Department of Biology, University of Florida, Gainesville, FL 32610, USA; Genetics Institute, University of Florida, Gainesville, FL 32610, USA; Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Alice C
authors.initials: AC
authors.lastname: Harmon
authors.affiliation: Department of Biology, University of Florida, Gainesville, FL 32610, USA; Genetics Institute, University of Florida, Gainesville, FL 32610, USA; Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL 32610, USA; Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL 32610, USA. Electronic address: schen@ufl.edu.
authors.forename: Sixue
authors.initials: S
authors.lastname: Chen
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D017360:Arabidopsis; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D029688:Brassica napus / Q000187:drug effects / Q000201:enzymology*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006861:Hydrogen Peroxide / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D010084:Oxidation-Reduction; D010766:Phosphorylation / Q000187:drug effects; D066329:Protein Aggregates / Q000235:genetics*; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D029681:Arabidopsis Proteins; D066329:Protein Aggregates; D017382:Reactive Oxygen Species; D000040:Abscisic Acid; D006861:Hydrogen Peroxide; C436292:AtMPK4 protein, Arabidopsis; D020928:Mitogen-Activated Protein Kinases
keywords: MAP kinase 4; Phosphorylation; Protein aggregation; ROS