3jv4
From Proteopedia
Revision as of 13:33, 4 May 2022
Crystal structure of the dimerization domains p50 and RelB
Structural highlights
Function[RELB_MOUSE] NF-kappa-B is a pleiotropic transcription factor which is present in almost all cell types and is involved in many biological processed such as inflammation, immunity, differentiation, cell growth, tumorigenesis and apoptosis. NF-kappa-B is a homo- or heterodimeric complex formed by the Rel-like domain-containing proteins RELA/p65, RELB, NFKB1/p105, NFKB1/p50, REL and NFKB2/p52. The dimers bind at kappa-B sites in the DNA of their target genes and the individual dimers have distinct preferences for different kappa-B sites that they can bind with distinguishable affinity and specificity. Different dimer combinations act as transcriptional activators or repressors, respectively. NF-kappa-B is controlled by various mechanisms of post-translational modification and subcellular compartmentalization as well as by interactions with other cofactors or corepressors. NF-kappa-B complexes are held in the cytoplasm in an inactive state complexed with members of the NF-kappa-B inhibitor (I-kappa-B) family. In a conventional activation pathway, I-kappa-B is phosphorylated by I-kappa-B kinases (IKKs) in response to different activators, subsequently degraded thus liberating the active NF-kappa-B complex which translocates to the nucleus. NF-kappa-B heterodimeric RelB-p50 and RelB-p52 complexes are transcriptional activators. RELB neither associates with DNA nor with RELA/p65 or REL. Stimulates promoter activity in the presence of NFKB2/p49 (By similarity). As a member of the NUPR1/RELB/IER3 survival pathway, may allow the development of pancreatic intraepithelial neoplasias.[1] [NFKB1_MOUSE] NF-kappa-B is a pleiotropic transcription factor present in almost all cell types and is the endpoint of a series of signal transduction events that are initiated by a vast array of stimuli related to many biological processes such as inflammation, immunity, differentiation, cell growth, tumorigenesis and apoptosis. NF-kappa-B is a homo- or heterodimeric complex formed by the Rel-like domain-containing proteins RELA/p65, RELB, NFKB1/p105, NFKB1/p50, REL and NFKB2/p52 and the heterodimeric p65-p50 complex appears to be most abundant one. The dimers bind at kappa-B sites in the DNA of their target genes and the individual dimers have distinct preferences for different kappa-B sites that they can bind with distinguishable affinity and specificity. Different dimer combinations act as transcriptional activators or repressors, respectively. NF-kappa-B is controlled by various mechanisms of post-translational modification and subcellular compartmentalization as well as by interactions with other cofactors or corepressors. NF-kappa-B complexes are held in the cytoplasm in an inactive state complexed with members of the NF-kappa-B inhibitor (I-kappa-B) family. In a conventional activation pathway, I-kappa-B is phosphorylated by I-kappa-B kinases (IKKs) in response to different activators, subsequently degraded thus liberating the active NF-kappa-B complex which translocates to the nucleus. NF-kappa-B heterodimeric p65-p50 and RelB-p50 complexes are transcriptional activators. The NF-kappa-B p50-p50 homodimer is a transcriptional repressor, but can act as a transcriptional activator when associated with BCL3. NFKB1 appears to have dual functions such as cytoplasmic retention of attached NF-kappa-B proteins by p105 and generation of p50 by a cotranslational processing. The proteasome-mediated process ensures the production of both p50 and p105 and preserves their independent function, although processing of NFKB1/p105 also appears to occur post-translationally. p50 binds to the kappa-B consensus sequence 5'-GGRNNYYCC-3', located in the enhancer region of genes involved in immune response and acute phase reactions. Plays a role in the regulation of apoptosis. Isoform 5, isoform 6 and isoform 7 act as inhibitors of transactivation of p50 NF-kappa-B subunit, probably by sequestering it in the cytoplasm. Isoform 3 (p98) (but not p84 or p105) acts as a transactivator of NF-kappa-B-regulated gene expression. In a complex with MAP3K8, NFKB1/p105 represses MAP3K8-induced MAPK signaling; active MAP3K8 is released by proteasome-dependent degradation of NFKB1/p105. Publication Abstract from PubMedTranscription factors of the nuclear factor kappaB (NF-kappaB) family arise through the combinatorial association of five distinct Rel subunits into functional dimers. However, not every dimer combination is observed in cells. The RelB subunit, for example, does not appear as a homodimer and forms heterodimers exclusively in combination with p50 or p52 subunits. We previously reported that the RelB homodimer could be forced to assemble through domain swapping in vitro. In order to understand the mechanism of selective dimerization among Rel subunits, we have determined the x-ray crystal structures of five RelB dimers. We find that RelB forms canonical side-by-side heterodimers with p50 and p52. We observe that, although mutation of four surface hydrophobic residues that are unique to RelB does not affect its propensity to form homodimers via domain swapping, alteration of two interfacial residues converts RelB to a side-by-side homodimer. Surprisingly, these mutant RelB homodimers remain distinct from canonical side-by-side NF-kappaB dimers in that the two monomers move away from one another along the 2-fold axis to avoid non-complementary interactions at the interface. The presence of distinct residues buried within the hydrophobic core of the RelB dimerization domain appears to influence the conformations of the surface residues that mediate the dimer interface. This conclusion is consistent with prior observations that alterations of domain core residues change dimerization propensity in the NF-kappaB family transcription factors. We suggest that RelB has evolved into a specialized NF-kappaB subunit with unique amino acids optimized for selective formation of heterodimers with p50 and p52. A Structural Basis for Selective Dimerization by NF-kappaB RelB.,Vu D, Huang DB, Vemu A, Ghosh G J Mol Biol. 2013 Feb 26. pii: S0022-2836(13)00122-8. doi:, 10.1016/j.jmb.2013.02.020. PMID:23485337[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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