Alternative titles; symbols
HGNC Approved Gene Symbol: AP2M1
Cytogenetic location: 3q27.1 Genomic coordinates (GRCh38): 3:184,174,855-184,184,091 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 3q27.1 | Intellectual developmental disorder 60 with seizures | 618587 | Autosomal dominant | 3 |
AP50 is a 50-kD component of the AP2 coat assembly protein complex of clathrin-coated vesicles. The complex consists of 2 large 100-kD components, which are called the alpha (601026) and beta (601025) subunits, a 50-kD component (AP50), and a small 17-kD protein (602242) (summary by Thurieau et al., 1988).
Thurieau et al. (1988) isolated AP50 cDNAs from rat brain mRNA and showed that the predicted 435-amino acid protein is highly conserved.
Druck et al. (1995) cloned the human homolog, which they designated CLAPM1, using a rat cDNA as a probe.
Liu et al. (1994) showed that AP50 is required for both in vitro assembly and activity of a vacuolar ATPase which may be responsible for proton pumping that occurs in the acidification of endosomes and lysosomes.
Krauss et al. (2006) found that the AP2 complex was a regulator of type I PIPK (see PIP5K1A; 603275)-mediated PtdIns(4,5)P2 synthesis in COS-7 and HeLa cells. AP2 via its mu-2 subunit directly interacted with the kinase core domain of the PIPK gamma-subunit (PIP5K1C; 606102) in vitro and in native protein extracts. Endocytic cargo protein binding to mu-2 stimulated PIPK activity. Krauss et al. (2006) concluded that there is a positive feedback loop consisting of endocytic cargo proteins, AP2M1, and PIPK type I, which may provide a specific pool of PtdIns(4,5)P2.
Druck et al. (1995) showed that the CLAPM1 gene contains 6 exons spanning about 8 kb of genomic DNA.
Druck et al. (1995) assigned CLAPM1 to chromosome 3 by hybridization with a panel of somatic cell hybrid DNAs and regionalized it by in situ hybridization to 3q28.
Gross (2019) mapped the AP2M1 gene to chromosome 3q27.1 based on an alignment of the AP2M1 sequence (GenBank BC014030) with the genomic sequence (GRCh38).
Crystal Structure
Kelly et al. (2014) determined a structure of AP2 that includes the clathrin-binding beta-2 hinge and developed an AP2-dependent budding assay. The authors found that an autoinhibitory mechanism prevents clathrin recruitment by cytosolic AP2. A large-scale conformational change driven by the plasma membrane phosphoinositide phosphatidylinositol 4,5-bisphosphate and cargo relieves this autoinhibition, triggering clathrin recruitment and hence clathrin-coated bud formation. Kelly et al. (2014) concluded that this molecular switching mechanism can couple AP2's membrane recruitment to its key functions of cargo and clathrin binding.
In 4 unrelated girls with autosomal dominant intellectual developmental disorder-60 with seizures (MRD60; 618587), Helbig et al. (2019) identified a recurrent de novo heterozygous missense mutation in the AP2M1 gene (R170W; 601024.0001). The mutation in the first 2 patients was found by whole-exome sequencing of 314 individuals with a similar phenotype; the 2 other patients were subsequently identified by whole-exome sequencing of 2,310 individuals with a similar phenotype. Presence of the mutation was confirmed by Sanger sequencing, and the variant was not found in the ExAC or gnomAD databases. Molecular modeling suggested that the mutation caused increased entropy in both the open and closed conformations of the AP2 complex, consistent with thermodynamic instability. In vitro functional expression studies in AP2M1-null HeLa cells and Ap2m1-null mouse astrocytes showed that the R170W variant caused reduced endocytosis compared to wildtype AP2M1, suggesting that the mutation adversely affects clathrin-mediated endocytosis, possibly by impaired recognition of cargo membrane proteins. The mutant protein was expressed at normal levels and localized properly to clathrin-coated pits. Helbig et al. (2019) noted that the AP2 complex mediates endocytic sorting of both presynaptic vesicle proteins and postsynaptic ion channels, and postulated that defective endocytic sorting of certain cargo membrane proteins and/or receptors in neurons may disrupt normal synaptic transmission.
In 4 unrelated girls with autosomal dominant intellectual developmental disorder-60 with seizures (MRD60; 618587), Helbig et al. (2019) identified a de novo heterozygous c.508C-T transition (c.508C-T, NM_004068.3) in the AP2M1 gene, resulting in an arg170-to-trp (R170W) substitution within a basic phospholipid-binding patch that is thought to stabilize the active open conformation of AP2 to aid in the association with cargo membrane proteins. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, was not found in the gnomAD or ExAC databases. Molecular modeling suggested that the mutation caused increased entropy in both the open and closed conformations of the AP2 complex, consistent with thermodynamic instability. In vitro functional expression studies in AP2M1-null HeLa cells and Ap2m1-null mouse astrocytes showed that the R170W variant caused reduced endocytosis compared to wildtype AP2M1, suggesting that the mutation adversely affects clathrin-mediated endocytosis, possibly by impaired recognition of cargo membrane proteins. The mutant protein was expressed at normal levels and localized properly to clathrin-coated pits.
Druck, T., Gu, Y., Prabhala. G., Cannizzaro, L. A., Park, S.-H., Huebner, K., Keen, J. H. Chromosome localization of human genes for clathrin adaptor polypeptides AP2-beta and AP50 and the clathrin-binding protein, VCP. Genomics 30: 94-97, 1995. [PubMed: 8595912] [Full Text: https://doi.org/10.1006/geno.1995.0016]
Gross, M. B. Personal Communication. Baltimore, Md. 9/19/2019.
Helbig, I., Lopez-Hernandez, T., Shor, O., Galer, P., Ganesan, S., Pendziwiat, M., Rademacher, A., Ellis, C. A., Humpfer, N., Schwarz, N., Seiffert, S., Peeden, J., and 15 others. A recurrent missense variant in AP2M1 impairs clathrin-mediated endocytosis and causes developmental and epileptic encephalopathy. Am. J. Hum. Genet. 104: 1060-1072, 2019. [PubMed: 31104773] [Full Text: https://doi.org/10.1016/j.ajhg.2019.04.001]
Kelly, B. T., Graham, S. C., Liska, N., Dannhauser, P. N., Honing, S., Ungewickell, E. J., Owen, D. J. AP2 controls clathrin polymerization with a membrane-activated switch. Science 345: 459-463, 2014. [PubMed: 25061211] [Full Text: https://doi.org/10.1126/science.1254836]
Krauss, M., Kukhtina, V., Pechstein, A., Haucke, V. Stimulation of phosphatidylinositol kinase type I-mediated phosphatidylinositol (4,5)-bisphosphate synthesis by AP-2 mu-cargo complexes. Proc. Nat. Acad. Sci. 103: 11934-11939, 2006. [PubMed: 16880396] [Full Text: https://doi.org/10.1073/pnas.0510306103]
Liu, Q., Feng, Y., Forgac, M. Activity and in vitro reassembly of the coated vesicle (H+)-ATPase requires the 50-kDa subunit of the clathrin assembly complex AP-2. J. Biol. Chem. 269: 31592-31597, 1994. [PubMed: 7989329]
Thurieau, C., Brosius, J., Burne, C., Jolles, P., Keen, J. H., Mattaliano, R. J., Chow, E. P., Ramachandran, K. L., Kirchhausen, T. Molecular cloning and complete amino acid sequence of AP50, an assembly protein associated with clathrin-coated vesicles. DNA 7: 663-669, 1988. [PubMed: 3148444] [Full Text: https://doi.org/10.1089/dna.1988.7.663]