Affinage

MKKS

Molecular chaperone MKKS · UniProt Q9NPJ1

Length
570 aa
Mass
62.3 kDa
Annotated
2026-04-28
28 papers in source corpus 11 papers cited in narrative 10 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

MKKS (BBS6) is a divergent Group II chaperonin-like protein that functions at the nexus of ciliogenesis, cytokinesis, and chromatin remodeling. It localizes to the pericentriolar material and dynamically shuttles between the centrosome and cytosol; its apical domain mediates centrosomal targeting, and RNAi depletion causes cytokinesis failure and ciliogenesis defects (PMID:15731008). MKKS forms a chaperonin co-complex with BBS10 and BBS12 that is required for BBSome assembly, and it physically interacts with CEP290 at the cilia transition zone/basal body to maintain multiprotein complex integrity (PMID:22446187, PMID:35373910). Disease-causing mutations lead to CHIP-dependent proteasomal degradation and centrosomal mislocalization (PMID:18094050); independently, MKKS shuttles into the nucleus where it binds the SWI/SNF subunit SMARCC1 to regulate gene expression, a cilia-independent function linked to congenital heart defects in McKusick-Kaufman syndrome (PMID:28753627). Loss-of-function mutations in MKKS cause Bardet-Biedl syndrome, with knockout mice exhibiting retinal degeneration, flagellar defects, obesity, and sensory deficits (PMID:10973251, PMID:15772095).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2000 Medium

    Positional cloning established that loss-of-function mutations in MKKS, encoding a chaperonin-like protein, are causative for Bardet-Biedl syndrome, providing the first gene-disease link and suggesting a protein-folding role.

    Evidence Linkage analysis and mutation screening in BBS patient pedigrees by two independent groups

    PMID:10973238 PMID:10973251

    Open questions at the time
    • Chaperonin folding function inferred from sequence homology only, not demonstrated biochemically
    • No target substrates identified
    • Subcellular localization unknown
  2. 2003 Medium

    Disease-associated BBS6 missense mutations cause dramatic protein mislocalization in mammalian cells, and heterozygous BBS6 alleles can modify disease severity at other BBS loci, establishing an oligogenic/epistatic mode of action.

    Evidence Mammalian cell transfection with patient allele and clinical genetic epistasis analysis

    PMID:12837689

    Open questions at the time
    • Mislocalization validated only in a single lab
    • Mechanism of epistatic interaction with other BBS loci undefined
    • Correct localization site not yet identified
  3. 2005 High

    MKKS was shown to localize to the pericentriolar material via its apical domain, to redistribute during mitosis, and to be essential for cytokinesis — resolving where the protein acts and providing the first cellular function beyond sequence-based predictions.

    Evidence Subcellular fractionation, live-cell imaging, RNAi knockdown, domain deletion and patient mutation mapping

    PMID:15731008

    Open questions at the time
    • No direct chaperonin activity demonstrated
    • Substrates at the centrosome unidentified
    • Mechanism linking centrosomal function to BBS disease phenotypes unclear
  4. 2005 High

    Mkks knockout mice phenocopied other BBS models — retinal degeneration, flagellar defects, obesity, and sensory deficits — confirming that complete MKKS loss underlies the full BBS phenotype in vivo.

    Evidence Knockout mouse with histology, retinal apoptosis, blood pressure, and behavioral assays

    PMID:15772095

    Open questions at the time
    • Molecular mechanism underlying each organ-specific phenotype not resolved
    • Whether phenotypes are cilia-dependent or -independent not distinguished
  5. 2007 High

    The fate of disease-causing MKKS mutants was explained: CHIP-dependent ubiquitin-proteasome degradation removes misfolded mutants, preventing their centrosomal accumulation, while wild-type MKKS dynamically shuttles between the centrosome and cytosol.

    Evidence Co-immunoprecipitation with CHIP/HSP70/HSP90, RNAi of CHIP, proteasome inhibition, live-cell FRAP-style shuttling analysis

    PMID:18094050

    Open questions at the time
    • Whether degradation of mutant protein is the primary pathogenic mechanism or loss of centrosomal function is not distinguished
    • No structural basis for mutant misfolding
  6. 2012 High

    MKKS was found to physically interact with CEP290 at the cilia transition zone/basal body, and genetic epistasis in zebrafish and mice showed their association governs multiprotein complex integrity and ciliogenesis — identifying a key protein partner and localizing MKKS function to the transition zone.

    Evidence Reciprocal Co-IP, zebrafish morpholino double knockdown, mouse double-mutant epistasis with ciliogenesis readouts

    PMID:22446187

    Open questions at the time
    • Stoichiometry and composition of the transition zone complex not defined
    • Whether MKKS chaperonin activity is required for CEP290 folding or assembly is unknown
  7. 2016 Medium

    The H395R mutation was shown to specifically disrupt MKKS–BBS12 interaction, linking reduced binding between these two chaperonin-like proteins to a limited retinitis pigmentosa/polydactyly phenotype and refining genotype-phenotype correlations.

    Evidence Co-immunoprecipitation in HEK-293T and ARPE-19 cells

    PMID:26900326

    Open questions at the time
    • Single method (Co-IP) without reciprocal validation or in vivo confirmation
    • Functional consequence of reduced BBS6–BBS12 binding on BBSome assembly not tested
  8. 2017 High

    A cilia-independent nuclear function was discovered: BBS6 shuttles into the nucleus, binds the SWI/SNF subunit SMARCC1, modulates its localization and downstream transcription, and the McKusick-Kaufman syndrome allele H84Y;A242S retains cilia function but is defective in nuclear transport — decoupling ciliopathy from cardiac defects.

    Evidence Nuclear-cytoplasmic fractionation, inducible transgenic zebrafish pulldown, transcriptional profiling, cilia functional assays

    PMID:28753627

    Open questions at the time
    • Direct target genes regulated by BBS6–SMARCC1 interaction not fully defined
    • Whether nuclear BBS6 acts as a chaperone for SMARCC1 or as a transcriptional cofactor is unresolved
    • Relevance to non-cardiac BBS phenotypes unknown
  9. 2022 Medium

    In vitro reconstitution confirmed that BBS6, together with BBS10 and BBS12, forms a chaperonin co-complex required for initial BBSome assembly — establishing the biochemical function long predicted from sequence homology.

    Evidence In vitro BBSome assembly reconstitution assay (described in review of prior work)

    PMID:35373910

    Open questions at the time
    • Primary experimental data cited indirectly via review
    • Individual contributions of BBS6 vs BBS10/BBS12 within the co-complex not delineated
    • No structural model of the co-complex

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include the structural basis for BBS6 chaperonin co-complex function, the full spectrum of substrates folded or assembled by BBS6, and how its dual centrosomal/nuclear roles are coordinately regulated.
  • No high-resolution structure of BBS6 alone or in the BBS chaperonin co-complex
  • Endogenous substrates beyond BBSome components and CEP290 not identified
  • Regulatory signals governing nuclear vs centrosomal partitioning unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0044183 protein folding chaperone 3
Localization
GO:0005815 microtubule organizing center 2 GO:0005634 nucleus 1 GO:0005829 cytosol 1 GO:0005929 cilium 1
Pathway
R-HSA-1852241 Organelle biogenesis and maintenance 3 R-HSA-392499 Metabolism of proteins 2 R-HSA-1640170 Cell Cycle 1
Partners
BBS12CEP290HSP90AA1HSPA8SMARCC1STUB1
Complex memberships
BBS chaperonin co-complex (BBS6/BBS10/BBS12)

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2005 MKKS/BBS6 is a divergent Group II chaperonin-like protein that does not oligomerize (unlike canonical chaperonins) and localizes predominantly to the pericentriolar material (PCM) surrounding centrioles; during interphase it is confined to the lateral surfaces of the PCM, but during mitosis it relocalizes throughout the PCM and to the intercellular bridge. Its predicted substrate-binding apical domain is sufficient for centrosomal association. Patient-derived mutations in this domain cause mislocalization. RNAi silencing of BBS6 leads to multinucleate, multicentrosomal cells with cytokinesis defects. Subcellular fractionation, live-cell imaging, RNAi knockdown, domain deletion/mutagenesis analysis, patient mutation functional testing Journal of cell science High 15731008
2007 Disease-causing MKKS mutants are rapidly degraded via the ubiquitin-proteasome pathway in a manner dependent on CHIP (HSC70-interacting protein), a chaperone-dependent ubiquitin ligase. Wild-type MKKS shuttles dynamically between the centrosome and cytosol, whereas rapidly degraded mutants fail to localize to the centrosome. CHIP and partner chaperones HSP70/HSC70 and HSP90 preferentially recognize MKKS mutants, and CHIP knockdown by RNAi moderately inhibits mutant degradation. Proteasome inhibition causes MKKS mutants to form insoluble structures at the centrosome. Live-cell imaging (centrosome shuttling), co-immunoprecipitation, RNAi knockdown of CHIP, proteasome inhibition assays, ubiquitination assays Molecular biology of the cell High 18094050
2012 The domain deleted in the CEP290rd16 allele directly interacts with MKKS; MKKS mutations identified in BBS patients disrupt this interaction. Combined subminimal knockdown of mkks and cep290 in zebrafish produced sensory defects, while combining Cep290rd16 and Mkks knockout alleles in mice paradoxically improved ciliogenesis and sensory function compared with either mutant alone, indicating that altered association of CEP290 and MKKS affects integrity of multiprotein complexes at the cilia transition zone and basal body. Co-immunoprecipitation (direct protein-protein interaction), zebrafish morpholino double knockdown epistasis, mouse double-mutant genetic epistasis, ciliogenesis assays The Journal of clinical investigation High 22446187
2017 BBS6 is actively transported between the cytoplasm and nucleus; the McKusick-Kaufman syndrome allele (BBS6-H84Y;A242S) maintains cilia function but is defective in nuclear-cytoplasmic transport. BBS6 interacts with the SWI/SNF chromatin remodeling protein SMARCC1 (Smarcc1a in zebrafish), modulates its subcellular localization, and produces similar transcriptional changes as smarcc1a manipulation. This identifies a cilia-independent nuclear function of BBS6 underlying congenital heart defects. Nuclear-cytoplasmic fractionation, inducible transgenic zebrafish BBS6 pulldown, protein-protein interaction studies, transcriptional profiling, cilia functional assays PLoS genetics High 28753627
2005 Mkks knockout mice exhibit retinal degeneration via apoptosis, failure of spermatozoa flagella formation, elevated blood pressure, hyperphagia-driven obesity, and olfactory/social deficits, phenocopying other BBS mouse models (Bbs2−/− and Bbs4−/−), establishing that complete loss of Mkks function underlies the BBS phenotype. Knockout mouse model, histology, retinal apoptosis assay, blood pressure measurement, behavioral testing Human molecular genetics High 15772095
2000 Loss-of-function mutations (frameshift, nonsense, missense) in the MKKS gene, which encodes a chaperonin-like protein, cause Bardet-Biedl syndrome; the data suggest that inability to fold a range of target proteins underlies the clinical manifestations. Positional cloning, mutation screening in patient pedigrees, linkage analysis Nature genetics Medium 10973238 10973251
2016 The H395R mutation in MKKS/BBS6 decreases the interaction of MKKS/BBS6 with BBS12, as demonstrated by protein-protein interaction studies in HEK-293T and ARPE-19 cells, linking disrupted BBS6–BBS12 interaction to a limited RP/polydactyly phenotype. Co-immunoprecipitation / protein-protein interaction studies in HEK-293T and ARPE-19 cells Molecular vision Medium 26900326
2003 A BBS6 missense mutation introduced in mammalian cells causes dramatic mislocalization of the protein compared with wild-type, and heterozygous BBS6 mutations can act as a third allele to potentiate disease severity in patients already carrying two recessive mutations at another BBS locus, demonstrating oligogenic/epistatic interaction. Mammalian cell transfection with patient-derived missense allele (mislocalization assay), clinical genetic epistasis analysis in patient families Human molecular genetics Medium 12837689
2022 BBS6 chaperonin-like protein is required for initial BBSome assembly in vitro; BBS6 together with BBS10 and BBS12 (all Group II chaperonin-like proteins) function as a chaperonin co-complex necessary for BBSome formation. In vitro BBSome assembly assay (reconstitution) American journal of medical genetics. Part C, Seminars in medical genetics Medium 35373910
2024 BBS6 functions as part of a TRiC/CCT-BBS chaperonin co-complex required for the localization of the adhesion GPCR ADGRV1 to the base of primary cilia; knockdown of BBS6 results in reduced ciliated cells and shorter primary cilia, and in the absence of this co-complex ADGRV1 is depleted from the ciliary base and degraded via the proteasome. RNAi knockdown, ciliogenesis quantification, proteasome inhibition assay, large-scale protein interaction network (ciliary proteome) bioRxivpreprint Low bio_10.1101_2024.10.31.621306

Source papers

Stage 0 corpus · 28 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2000 Mutations in MKKS cause obesity, retinal dystrophy and renal malformations associated with Bardet-Biedl syndrome. Nature genetics 241 10973251
2000 Mutations in MKKS cause Bardet-Biedl syndrome. Nature genetics 209 10973238
2005 Mkks-null mice have a phenotype resembling Bardet-Biedl syndrome. Human molecular genetics 161 15772095
2003 Heterozygous mutations in BBS1, BBS2 and BBS6 have a potential epistatic effect on Bardet-Biedl patients with two mutations at a second BBS locus. Human molecular genetics 153 12837689
2005 MKKS/BBS6, a divergent chaperonin-like protein linked to the obesity disorder Bardet-Biedl syndrome, is a novel centrosomal component required for cytokinesis. Journal of cell science 137 15731008
2012 Combining Cep290 and Mkks ciliopathy alleles in mice rescues sensory defects and restores ciliogenesis. The Journal of clinical investigation 67 22446187
2001 Genetic and mutational analyses of a large multiethnic Bardet-Biedl cohort reveal a minor involvement of BBS6 and delineate the critical intervals of other loci. American journal of human genetics 60 11179009
2002 Mutation analysis of the MKKS gene in McKusick-Kaufman syndrome and selected Bardet-Biedl syndrome patients. Human genetics 49 12107442
2010 LRRK2 and the stress response: interaction with MKKs and JNK-interacting proteins. Neuro-degenerative diseases 46 20173330
2010 Molecular diagnosis reveals genetic heterogeneity for the overlapping MKKS and BBS phenotypes. European journal of medical genetics 34 21044901
2017 Nuclear/cytoplasmic transport defects in BBS6 underlie congenital heart disease through perturbation of a chromatin remodeling protein. PLoS genetics 28 28753627
2019 Matrine Suppresses Reactive Oxygen Species (ROS)-Mediated MKKs/p38-Induced Inflammation in Oxidized Low-Density Lipoprotein (ox-LDL)-Stimulated Macrophages. Medical science monitor : international medical journal of experimental and clinical research 25 31156213
2007 MKKS is a centrosome-shuttling protein degraded by disease-causing mutations via CHIP-mediated ubiquitination. Molecular biology of the cell 21 18094050
2022 Bardet-Biedl syndrome: The pleiotropic role of the chaperonin-like BBS6, 10, and 12 proteins. American journal of medical genetics. Part C, Seminars in medical genetics 18 35373910
2016 A novel H395R mutation in MKKS/BBS6 causes retinitis pigmentosa and polydactyly without other findings of Bardet-Biedl or McKusick-Kaufman syndrome. Molecular vision 14 26900326
2005 No evidence for triallelic inheritance of MKKS/BBS loci in Amish Mckusick-Kaufman syndrome. American journal of medical genetics. Part A 12 16104012
2018 Novel ASK1 Inhibitor AGI-1067 Attenuates AGE-Induced Fibrotic Response by Suppressing the MKKs/p38 MAPK Pathway in Human Coronary Arterial Smooth Muscle Cells. International heart journal 10 30305582
2008 Association between BBS6/MKKS gene polymorphisms, obesity and metabolic syndrome in the Greek population. International journal of obesity (2005) 10 18813213
2017 Phylogenomic analysis of MKKs and MAPKs from 16 legumes and detection of interacting pairs in chickpea divulge MAPK signalling modules. Scientific reports 9 28694440
2021 Novel Compound Heterozygous BBS2 and Homozygous MKKS Variants Detected in Chinese Families with Bardet-Biedl Syndrome. Journal of ophthalmology 7 33520300
2019 Two novel MKKs (MKK4 and MKK7) from Ctenopharyngodon idella are involved in the intestinal immune response to bacterial muramyl dipeptide challenge. Developmental and comparative immunology 7 30633955
2018 Novel ASK1 inhibitor AGI-1067 improves AGE-induced cardiac dysfunction by inhibiting MKKs/p38 MAPK and NF-κB apoptotic signaling. FEBS open bio 7 30186746
2022 Novel Mutations in the MKKS, BBS7, and ALMS1 Genes in Iranian Children with Clinically Suspected Bardet-Biedl Syndrome. Case reports in ophthalmological medicine 6 35912300
2022 Behavioral Phenotyping of Bbs6 and Bbs8 Knockout Mice Reveals Major Alterations in Communication and Anxiety. International journal of molecular sciences 6 36498834
2020 Legg-Calvé-Perthes disease in a patient with Bardet-Biedl syndrome: A case report of a novel MKKS/BBS6 mutation. Clinical case reports 3 33363891
2022 [Genetic analysis of novel MKKS variants in a Chinese patient with Bardet-Biedl syndrome]. Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics 2 35810436
2020 Novel mutation in MKKS/BBS6 linked with arRP and polydactyly in a family of North Indian origin. Clinical & experimental ophthalmology 1 31989739
2025 Assessment of genetic variation(s) in BBS10, BBS6, and BBS12 in a family from Sindh, Pakistan diagnosed with Bardet-Biedl Syndrome. JPMA. The Journal of the Pakistan Medical Association 0 41418239