9lgs
From Proteopedia
R-degron fused ZZ-domain of the Arabidopsis thaliana E3 ubiquitin-protein ligase BIG
Structural highlights
FunctionBIG_ARATH Required for auxin efflux and polar auxin transport (PAT) influencing auxin-mediated developmental responses (e.g. cell elongation, apical dominance, lateral root production, inflorescence architecture, general growth and development). Controls the elongation of the pedicels and stem internodes through auxin action. Involved in the expression modulation of light-regulated genes. Represses CAB1 and CAB3 genes expression in etiolated seedlings. Confers sensitivity to the auxin transport inhibitors N-1-naphthylphthalamic acid (NPA), 2-carboxyphenyl-3-phenylpropane-l,2-dione (CPD), and methyl-2-chloro-9-hydroxyfluorene-9-carboxylate (CFM). Influences the polarized subcellular distribution of the auxin transporter PIN1 in response to auxin transport inhibitors. Plays a role in the regulation of responses to phytohormones such as auxin, cytokinins, ethylene and gibberellic acid (GA), particularly during light-mediated stimuli (e.g. shade ovoidance, etiolation). Required for pericycle cell activation to form lateral root primordia (LRP) in both high and low phosphate P conditions. Necessary for the plant-growth promotion and lateral root development mediated by the fungus Trichoderma virens.[1] [2] [3] [4] [5] [6] [7] [8] [9] Publication Abstract from PubMedEukaryotic cells have evolved sophisticated quality control mechanisms to eliminate aggregation-prone proteins that compromise cellular health. Central to this defense is the ubiquitin-proteasome system, where UBR4 acts as an essential E4 ubiquitin ligase, amplifying degradation marks on defective proteins. Cryo-electron microscopy analysis of UBR4 in complex with its cofactors KCMF1 and CALM1 reveals a massive 1.3-megadalton ring structure, featuring a central substrate-binding arena and flexibly attached catalytic units. Our structure shows how UBR4 binds substrate and extends lysine-48-specific ubiquitin chains. Efficient substrate targeting depends on both preubiquitination and specific N-degrons, with KCMF1 acting as a key substrate filter. The architecture of the E4 megacomplex is conserved across eukaryotes, but species-specific adaptations allow UBR4 to perform its precisely tuned quality control function in diverse cellular environments. Architecture of the UBR4 complex, a giant E4 ligase central to eukaryotic protein quality control.,Grabarczyk DB, Ehrmann JF, Murphy P, Yang WS, Kurzbauer R, Bell LE, Deszcz L, Neuhold J, Schleiffer A, Shulkina A, Lee J, Shin JS, Meinhart A, Versteeg GA, Zavodszky E, Song HK, Hegde RS, Clausen T Science. 2025 Aug 28;389(6763):909-914. doi: 10.1126/science.adv9309. Epub 2025 , Aug 28. PMID:40875847[10] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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