Affinage

CHN2

Beta-chimaerin · UniProt P52757

Round 2 corrected
Length
468 aa
Mass
53.9 kDa
Annotated
2026-04-28
40 papers in source corpus 12 papers cited in narrative 12 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

CHN2 encodes β2-chimaerin, a Rac1-specific GTPase-activating protein (RacGAP) that converts Rac1-GTP to its inactive GDP-bound state, thereby attenuating Rac-dependent proliferative, migratory, and mitogenic signaling cascades (PMID:12877655, PMID:15863513). In its resting state, the protein is autoinhibited: crystallography revealed that the N-terminus occludes the RacGAP catalytic site while the C1 domain lipid-binding pocket is buried by intramolecular contacts, and diacylglycerol or phorbol ester binding to the C1 domain triggers cooperative unfolding of these autoinhibitory interactions, membrane translocation to the Golgi (via the anchor protein Tmp21-I), and enzymatic activation (PMID:15507211, PMID:9334226, PMID:11689559). Active β2-chimaerin suppresses Rac1-GTP levels downstream of ErbB receptors, reducing cyclin D1 expression, Rb phosphorylation, and ERK activation to enforce G1 cell cycle arrest in breast cancer cells (PMID:15863513, PMID:16428439). Heterozygous disruption of CHN2 by chromosomal translocation, combined with INSR haploinsufficiency, causes insulin resistance and intrauterine growth deficiency, implicating β2-chimaerin in proximal insulin signaling in vivo (PMID:19720790).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 1994 High

    Identification of β2-chimaerin as a novel RacGAP with an SH2 domain resolved the question of what protein product the alternatively spliced CHN2 locus encodes and established its neuronal enrichment.

    Evidence cDNA cloning, immunoblotting, subcellular fractionation, and immunohistochemistry in rat cerebellum

    PMID:8175705

    Open questions at the time
    • Mechanism of SH2 domain function in β2-chimaerin remained undefined
    • Regulation of GAP activity was unknown
    • Expression and role outside the nervous system not explored
  2. 1997 High

    Demonstrating high-affinity phorbol ester binding (Kd ~1.9 nM) via the C1 domain and phorbol-ester-induced translocation established β2-chimaerin as a non-PKC diacylglycerol/phorbol ester receptor, answering how lipid second messengers regulate this RacGAP.

    Evidence Baculovirus-expressed protein, quantitative [³H]PDBu binding with Scatchard analysis, subcellular fractionation in COS-7 cells

    PMID:9334226

    Open questions at the time
    • Structural basis of autoinhibition and lipid-dependent activation unresolved
    • Identity of membrane compartment targeted upon translocation not yet determined
  3. 2001 Medium

    Mapping the translocation target to the Golgi apparatus and identifying Tmp21-I as a C1-domain-dependent anchoring partner resolved where β2-chimaerin acts after lipid activation and how it is positionally retained.

    Evidence BODIPY-TR-ceramide Golgi co-staining, yeast two-hybrid screen, co-immunoprecipitation, deletional and site-directed mutagenesis

    PMID:11278894 PMID:11689559

    Open questions at the time
    • Tmp21-I interaction shown by Y2H and Co-IP in a single lab; independent validation lacking
    • Functional consequence of Golgi-localized RacGAP activity not tested
  4. 2004 High

    The 3.2 Å crystal structure revealed the full allosteric mechanism: the N-terminus physically blocks the GAP active site while the C1 lipid-binding pocket is buried, and DAG/phorbol ester binding cooperatively disrupts these contacts, explaining how lipid signals convert the enzyme from an autoinhibited to an active state.

    Evidence X-ray crystallography of full-length β2-chimaerin at 3.2 Å resolution

    PMID:15507211

    Open questions at the time
    • No structure of the activated, Rac-bound complex available
    • Role of the SH2 domain in autoinhibition or substrate engagement unclear
  5. 2005 High

    Functional studies in breast cancer cells demonstrated that β2-chimaerin's RacGAP activity causes G1 arrest by reducing cyclin D1 and Rb phosphorylation, with epistasis showing Rac1 (not RhoA) as the specific downstream target, establishing the biological output of this GAP.

    Evidence Adenoviral expression in MCF-7 cells, Rac-GTP pulldown, flow cytometry, immunoblotting, constitutively active Rac1 rescue

    PMID:15863513

    Open questions at the time
    • Whether endogenous β2-chimaerin loss drives tumor progression not directly tested
    • Relevance beyond breast cancer cell lines unknown
  6. 2006 High

    Placing β2-chimaerin downstream of ErbB3/ErbB2–PI3K–Rac signaling and showing it blocks heregulin-induced ERK activation and mitogenicity defined the receptor-to-GAP pathway axis it antagonizes.

    Evidence Rac-GTP pulldown, ErbB receptor inhibitors and RNAi, β2-chimaerin overexpression, ERK activity and proliferation/migration assays in breast cancer cells

    PMID:16428439

    Open questions at the time
    • Direct recruitment mechanism from ErbB receptors to β2-chimaerin not identified
    • SH2 domain role in receptor-proximal signaling not addressed
  7. 2009 Medium

    A natural human chromosomal translocation disrupting one CHN2 allele, combined with INSR haploinsufficiency, produced insulin resistance and growth deficiency, providing the first in vivo evidence that β2-chimaerin participates in insulin signaling.

    Evidence FISH breakpoint mapping, gene expression in patient-derived adipose tissue, clinical phenotyping of translocation carriers

    PMID:19720790

    Open questions at the time
    • CHN2 haploinsufficiency effect confounded by concurrent INSR haploinsufficiency; isolated CHN2 role not separable
    • Molecular mechanism linking Rac-GAP activity to insulin signal transduction not defined
  8. 2020 Medium

    Systems-level characterization confirmed β2-chimaerin's widespread autoinhibition and revealed that RhoGAPs including CHN2 are more promiscuous than GEFs and shape Rac1 activity gradients by spatial segregation at integrin adhesions, contextualizing CHN2 within the broader Rho signaling network.

    Evidence Family-wide substrate specificity assays, AP-MS interactomics, subcellular localization profiling, RAC1 biosensors with mechanical stimulation

    PMID:32203420

    Open questions at the time
    • CHN2-specific interactors and substrates not individually resolved in this family-wide study
    • Extent of promiscuity of β2-chimaerin toward GTPases other than Rac1 not quantitatively defined

Open questions

Synthesis pass · forward-looking unresolved questions
  • Major open questions remain: the SH2 domain's specific binding partners and contribution to signaling or autoinhibition are undefined, no activated/Rac-bound structure exists, and the physiological role of β2-chimaerin in insulin signaling independent of INSR requires validation in animal models.
  • SH2 domain function uncharacterized despite being a distinguishing feature of β2-chimaerin
  • No structure of Rac1-bound activated complex
  • In vivo role in insulin signaling confounded by co-disruption of INSR

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 4 GO:0003924 GTPase activity 3 GO:0008289 lipid binding 3 GO:0140096 catalytic activity, acting on a protein 3
Localization
GO:0005794 Golgi apparatus 2 GO:0005829 cytosol 2 GO:0005886 plasma membrane 1
Pathway
R-HSA-162582 Signal Transduction 5 R-HSA-1640170 Cell Cycle 1
Partners
ERBB2ERBB3RAC1TMED10

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1994 β2-chimaerin (CHN2) was identified as a 46-kDa RacGAP protein specifically expressed in cerebellar granule cells, possessing an N-terminal SH2 domain generated by alternative splicing of the beta-chimaerin gene. It is enriched in particulate/synaptosomal fractions and its expression increases postnatally. cDNA cloning, PCR, immunoblotting, subcellular fractionation, immunohistochemistry in rat cerebellum and mouse weaver mutant The Journal of biological chemistry High 8175705
1995 Human β2-chimaerin is a 468-amino acid GTPase-activating protein for p21Rac, localized to chromosome 7p15.3, expressed at high levels in brain and pancreas, and down-regulated in high-grade glioblastoma compared to normal brain and low-grade astrocytoma. RT-PCR, FISH chromosomal mapping, RNase protection assay, expression profiling in human tissues and tumors Cancer research Medium 7614486
1997 β2-chimaerin binds phorbol esters with high affinity (Kd ~1.9 nM) via its C1 domain in a phosphatidylserine-dependent manner, and translocates from cytosolic to particulate fractions upon phorbol ester treatment in COS-7 cells, establishing it as a novel non-PKC phorbol ester receptor. Baculovirus expression in Sf9 cells, [3H]phorbol 12,13-dibutyrate binding assay (Scatchard analysis), subcellular fractionation after phorbol ester treatment The Journal of biological chemistry High 9334226
1999 β2-chimaerin is a high-affinity diacylglycerol (DAG) receptor via its C1 domain; conformationally constrained DAG lactone analogs bind with >100-fold higher affinity than 1-oleoyl-2-acetylglycerol. DAG binding induces translocation to the perinuclear region, and mutation of the conserved Cys-246 in the C1 domain abolishes both binding and translocation. Binding assays with DAG lactone analogs, GFP-fusion protein imaging (live cell microscopy), site-directed mutagenesis of C1 domain Cys-246, subcellular fractionation Proceedings of the National Academy of Sciences of the United States of America High 10518540
2001 Phorbol ester-induced translocation of β2-chimaerin from cytosol to the Golgi apparatus is entirely dependent on the C1 domain (shown by deletional analysis and mutagenesis). Phorbol esters also promote association of β2-chimaerin with Rac in cells, and chimaerin isoforms (α1, β1, β2) share this C1-dependent translocation mechanism. Subcellular fractionation, fluorescence co-staining with Golgi marker BODIPY-TR-ceramide, deletional analysis, site-directed mutagenesis, co-immunoprecipitation with Rac The Journal of biological chemistry High 11278894
2001 β2-chimaerin associates with Tmp21-I (p23), a Golgi-localized anchoring protein, through its C1 domain in a PKC-independent manner. Phorbol esters promote both β2-chimaerin translocation to the perinuclear region and its interaction with Tmp21-I, identifying Tmp21-I as a positional anchor for β2-chimaerin at the Golgi. Yeast two-hybrid screen to identify interacting proteins, co-immunoprecipitation, deletional analysis of C1 domain requirement The Journal of biological chemistry Medium 11689559
2003 β2-chimaerin has Rac-GAP activity specifically for Rac1 (not Cdc42 or RhoA); acidic phospholipids markedly enhance its catalytic activity in vitro. β2-chimaerin reduces cellular Rac-GTP levels and impairs EGF-induced GTP loading onto Rac in COS-1 cells. Deletional and mutagenesis analysis demonstrated that the GAP domain is essential for Rac inactivation. Phorbol ester (PMA) has a dual effect: it increases Rac-GTP levels via PKC, but under PKC inhibition, PMA potentiates β2-chimaerin's Rac-inactivating effect. β2-chimaerin co-localizes and co-immunoprecipitates with active Rac at the plasma membrane. In vitro GAP activity assay with acidic phospholipids, Rac-GTP pulldown (PAK-PBD) in COS-1 cells, deletional analysis and mutagenesis, co-immunoprecipitation, fluorescence co-localization The Biochemical journal High 12877655
2004 Crystal structure of β2-chimaerin at 3.2 Å resolution revealed its inactive conformation: the N-terminus protrudes into the active site of the RacGAP domain, sterically blocking Rac binding. The diacylglycerol/phospholipid binding site on the C1 domain is buried by contacts with the N-terminus, SH2 domain, RacGAP domain, and SH2-C1 linker. Phospholipid binding to the C1 domain triggers cooperative dissociation of these autoinhibitory interactions, allowing the N-terminus to move out of the active site and activate the enzyme — defining the structural mechanism of lipid-dependent allosteric activation. X-ray crystallography at 3.2 Å resolution of the full-length β2-chimaerin protein Cell High 15507211
2005 β2-chimerin inhibits breast cancer cell proliferation and induces G1 cell cycle arrest via its Rac-GAP domain. Adenoviral expression of β2-chimerin in MCF-7 cells reduced Rac-GTP levels, decreased cyclin D1 expression, and caused retinoblastoma protein dephosphorylation. Cells stably expressing constitutively active Rac (V12Rac1), but not RhoA (V14RhoA), were resistant to β2-chimerin-induced cell cycle arrest, establishing Rac as the specific effector. Adenoviral gene delivery, Rac-GTP pulldown assay, flow cytometry (cell cycle analysis), immunoblotting for cyclin D1 and Rb phosphorylation, stable expression of dominant-active Rac1/RhoA mutants (epistasis) The Journal of biological chemistry High 15863513
2006 β2-chimerin's Rac-GAP activity suppresses heregulin β1 (HRG)-induced ERK activation, mitogenicity, and migration in breast cancer cells. HRG activates Rac through ErbB3/ErbB2 and via transactivation of EGFR (not ErbB4), in a PI3K-dependent, Src-independent manner, and Rac is a critical mediator of this mitogenic signaling; expression of β2-chimerin (inactivating Rac) blocks these responses. Rac-GTP pulldown assay, ErbB receptor-specific inhibitors and RNAi knockdown, β2-chimerin overexpression, ERK activity assay, cell proliferation and migration assays Molecular and cellular biology High 16428439
2009 CHN2 (encoding β2-chimerin) is expressed in insulin-sensitive tissues including adipose tissue, and heterozygous disruption of CHN2 by chromosomal translocation t(7;19)(p15.2;p13.2) results in decreased CHN2 gene expression in patient-derived adipose tissue. Combined haploinsufficiency of CHN2 and INSR causes insulin resistance and intrauterine growth deficiency, implicating CHN2 as a component of proximal insulin signaling in vivo. FISH breakpoint mapping, gene sequencing, expression studies in patient-derived adipose tissue (gene expression assay), clinical phenotyping of translocation carriers Diabetes Medium 19720790
2020 In a systems-level family-wide characterization of RhoGAPs, β2-chimaerin (CHN2) was shown to be widely autoinhibited, to form complexes with other Rho regulators for joint network coordination, and to provide positional information for RAC1 signaling. RhoGAPs (including β2-chimaerin) are more promiscuous than RhoGEFs in substrate specificity, serving to confine Rac activity gradients. Integrin adhesions were shown to spatially segregate GEFs and GAPs to shape RAC1 activity zones. Family-wide substrate specificity assays, interactome mapping (affinity-purification MS), subcellular localization profiling, RAC1 activity biosensors in cells with mechanical stimulation Nature cell biology Medium 32203420

Source papers

Stage 0 corpus · 40 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2005 A human protein-protein interaction network: a resource for annotating the proteome. Cell 1704 16169070
2002 Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. Proceedings of the National Academy of Sciences of the United States of America 1479 12477932
2017 Architecture of the human interactome defines protein communities and disease networks. Nature 1085 28514442
2020 A reference map of the human binary protein interactome. Nature 849 32296183
2003 Complete sequencing and characterization of 21,243 full-length human cDNAs. Nature genetics 754 14702039
2021 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. Cell 705 33961781
2011 Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium. Briefings in bioinformatics 656 21873635
2005 A quantitative protein interaction network for the ErbB receptors using protein microarrays. Nature 568 16273093
2005 High-throughput mapping of a dynamic signaling network in mammalian cells. Science (New York, N.Y.) 553 15761153
2004 The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC). Genome research 438 15489334
2005 Diversification of transcriptional modulation: large-scale identification and characterization of putative alternative promoters of human genes. Genome research 409 16344560
1996 Normalization and subtraction: two approaches to facilitate gene discovery. Genome research 401 8889548
2012 Novel genetic loci identified for the pathophysiology of childhood obesity in the Hispanic population. PloS one 312 23251661
2020 Systems analysis of RhoGEF and RhoGAP regulatory proteins reveals spatially organized RAC1 signalling from integrin adhesions. Nature cell biology 194 32203420
2008 Molecular genetics of successful smoking cessation: convergent genome-wide association study results. Archives of general psychiatry 194 18519826
2003 The DNA sequence of human chromosome 7. Nature 188 12853948
2003 Human chromosome 7: DNA sequence and biology. Science (New York, N.Y.) 154 12690205
2010 Personalized smoking cessation: interactions between nicotine dose, dependence and quit-success genotype score. Molecular medicine (Cambridge, Mass.) 108 20379614
2004 Structural mechanism for lipid activation of the Rac-specific GAP, beta2-chimaerin. Cell 105 15507211
1999 beta2-chimaerin is a novel target for diacylglycerol: binding properties and changes in subcellular localization mediated by ligand binding to its C1 domain. Proceedings of the National Academy of Sciences of the United States of America 90 10518540
1997 Beta2-chimaerin is a high affinity receptor for the phorbol ester tumor promoters. The Journal of biological chemistry 90 9334226
2003 Characterization of the Rac-GAP (Rac-GTPase-activating protein) activity of beta2-chimaerin, a 'non-protein kinase C' phorbol ester receptor. The Biochemical journal 82 12877655
1999 Trypanosoma brucei: killing of bloodstream forms in vitro and in vivo by the cysteine proteinase inhibitor Z-phe-ala-CHN2. Experimental parasitology 72 10092476
2005 Rac-GAP-dependent inhibition of breast cancer cell proliferation by {beta}2-chimerin. The Journal of biological chemistry 69 15863513
2006 Essential role for Rac in heregulin beta1 mitogenic signaling: a mechanism that involves epidermal growth factor receptor and is independent of ErbB4. Molecular and cellular biology 68 16428439
2001 Phorbol esters and related analogs regulate the subcellular localization of beta 2-chimaerin, a non-protein kinase C phorbol ester receptor. The Journal of biological chemistry 66 11278894
2015 Phospho-tyrosine dependent protein-protein interaction network. Molecular systems biology 61 25814554
2023 Cross-linking mass spectrometry discovers, evaluates, and corroborates structures and protein-protein interactions in the human cell. Proceedings of the National Academy of Sciences of the United States of America 60 37071682
1994 Cerebellar beta 2-chimaerin, a GTPase-activating protein for p21 ras-related rac is specifically expressed in granule cells and has a unique N-terminal SH2 domain. The Journal of biological chemistry 59 8175705
1995 Identification and characterization of human beta 2-chimaerin: association with malignant transformation in astrocytoma. Cancer research 54 7614486
2007 The crystal structure of human dipeptidyl peptidase I (cathepsin C) in complex with the inhibitor Gly-Phe-CHN2. The Biochemical journal 53 17020538
2001 Chimaerins, novel non-protein kinase C phorbol ester receptors, associate with Tmp21-I (p23): evidence for a novel anchoring mechanism involving the chimaerin C1 domain. The Journal of biological chemistry 53 11689559
1994 In vitro embryotoxicity of the cysteine proteinase inhibitors benzyloxycarbonyl-phenylalanine-alanine-diazomethane (Z-Phe-Ala-CHN2) and benzyloxycarbonyl-phenylalanine-phenylalanine-diazomethane (Z-Phe-Phe-CHN2). Teratology 26 7871486
2009 Severe insulin resistance and intrauterine growth deficiency associated with haploinsufficiency for INSR and CHN2: new insights into synergistic pathways involved in growth and metabolism. Diabetes 22 19720790
2007 The cysteine proteinase inhibitor Z-Phe-Ala-CHN2 alters cell morphology and cell division activity of Trypanosoma brucei bloodstream forms in vivo. Kinetoplastid biology and disease 20 17328798
2019 Efficacy and Safety of Dulaglutide Versus Insulin Glargine in Chinese T2DM Patients: A Subgroup Analysis of a Randomized Trial (AWARD-CHN2). Diabetes therapy : research, treatment and education of diabetes and related disorders 13 31228090
2017 CHN2 Promoter Methylation Change May Be Associated With Methamphetamine Dependence. Shanghai archives of psychiatry 11 29719347
2013 Association of a novel polymorphism of the β2-chimaerin gene (CHN2) with smoking. Journal of investigative medicine : the official publication of the American Federation for Clinical Research 9 23941981
2023 Neuroprotective and Antioxidant Properties of CholesteroNitrone ChN2 and QuinolylNitrone QN23 in an Experimental Model of Cerebral Ischemia: Involvement of Necrotic and Apoptotic Cell Death. Antioxidants (Basel, Switzerland) 5 37507904
2021 Efficacy of Dulaglutide in Chinese Patients with Type 2 Diabetes and Different Glycemic Patterns: a Post-hoc Analysis of the Phase 3 AWARD-CHN2 Trial. Diabetes therapy : research, treatment and education of diabetes and related disorders 0 34870792