Phosphorylation Extracellular Signal Regulated Kinase 1/2 (P-ERK1/2) ELISA Kit for Sheep

Encodes a plasma membrane localized leucine-rich repeat receptor kinase involved in brassinosteroid signal transduction. BRI1 ligand is brassinolide which binds at the extracellular domain. Binding results in phosphorylation of the kinase domain which activates the BRI1 protein leading to BR responses. Residue T-1049 and either S-1044 or T-1045 were essential for kinase function in vitro and normal BRI1 signaling in planta. Although BAK1 and BRI1 alone localize in the plasma membrane, when BAK1 and BRI1 are coexpressed, the heterodimer BAK1/BRI1 they form is localized in the endosome. BRI1 appears to be involved in the autonomous pathway that regulates the transition to flowering, primarily through its effects on FLC expression levels, as uncovered by double mutant analyses. This most likely occurs as a result of BRI1-dependent effects on histone acetylation, but not histone triMeH3K4 methylation, at the FLC locus.

Function: Receptor with a dual specificity kinase activity acting on both serine/threonine- and tyrosine-containing substrates. Regulates, in response to brassinosteroid binding, a signaling cascade involved in plant development, including expression of light- and stress-regulated genes, promotion of cell elongation, normal leaf and chloroplast senescence, and flowering. Binds brassinolide, and less effectively castasterone, but not 2,3,22,23-O-tetramethylbrassinolide or ecdysone. May be involved in a feedback regulation of brassinosteroid biosynthesis. Phosphorylates BRI1-associated receptor kinase 1 (BAK1), Transthyretin-Like protein (TTL) and SERK1 on 'Ser-299' and 'Thr-462' in vitro. May have a guanylyl cyclase activity. Ref.2 Ref.3 Ref.16 Ref.19 Ref.22 Ref.24

Catalytic activity: ATP + a protein = ADP + a phosphoprotein.ATP + a [protein]-L-tyrosine = ADP + a [protein]-L-tyrosine phosphate.

Enzyme regulation: Activated by Ser and Thr phosphorylation.

Subunit structure: Monomer or homodimer in the plasma membrane. Heterodimer with BAK1 in the endosomes. Interacts with SERK1 and TTL in a kinase-dependent manner. Component of the SERK1 signaling complex, composed of KAPP, CDC48A, GRF6 or GRF7, SERK1, SERK2, SERK3/BAK1 and BRI1. Ref.10 Ref.11 Ref.12 Ref.13 Ref.14 Ref.15 Ref.20 Ref.22

Subcellular location: Cell membrane; Single-pass type I membrane protein. Endosome membrane; Single-pass type I membrane protein Ref.3 Ref.9 Ref.10 Ref.12 Ref.17 Ref.18.

Tissue specificity: Expressed ubiquitously. Ref.1 Ref.3

Developmental stage: Expressed constitutively in either dark- or light-grown seedlings.

Domain: Contains one leucine-zipper motif and two pairs of conservatively spaced Cys (Cys pair 1 and 2) involved in forming heterodimers. Ref.19A 70 amino acid island between the 20th and the 21th LRR is essential for the binding of brassinosteroids. Ref.19The JM domain (815-883) is a positive regulator of kinase activity and is required for Tyr phosphorylation. Ref.19A guanylyl cyclase domain (1021-1134) having an in vitro activity is included in the C-terminal kinase domain. Ref.19

Post-translational modification: Autophosphorylated on Tyr-831, Tyr-956 and maybe Tyr-1072. Phosphorylated on at least 12 sites, with a preference for Ser residues. Transphosphorylated on Ser-887 by SERK1 and on Ser-838, Thr-846, Ser-858 and Ser-1166 by BAK1. Phosphorylation on Ser-1166 enhances the kinase activity. Ref.7 Ref.9 Ref.10 Ref.11 Ref.14 Ref.22 Ref.23 Ref.24Glycosylated. Ref.18

Disruption phenotype: Dwarf phenotype and aberrant leaf shape. Ref.2

Miscellaneous: Binding of brassinosteroid induces intramolecular autophosphorylation of BRI1. Interaction with BAK1 activates both receptor kinases and the full activation of either receptor kinase requires transphosphorylation by their partners. Optimum in vitro phosphorylation of the substrate requires Arg or Lys residues at P-3, P-4, and P+5 (relative to the phosphorylated amino acid at P=0). Homodimerizes in the absence of ligand and binds brassinosteroid in the absence of its coreceptor BAK1.The bri1-9 mutation produces a fully active protein with a subtle conformational change that is recognized for reglucosylation by UGGT, resulting in its endoplasmic reticulum retention via Glc1Man9GlcNAc(2)-calreticulin/calnexin interaction (Ref.18).

Sequence similarities: Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.Contains 25 LRR (leucine-rich) repeats.Contains 1 protein kinase domain.