AP4M1
Function
Component of the adaptor protein complex 4 (AP-4). Adaptor protein complexes are vesicle coat components involved both in vesicle formation and cargo selection. They control the vesicular transport of proteins in different trafficking pathways (PubMed:10066790, PubMed:10436028, PubMed:11139587, PubMed:11802162, PubMed:20230749). AP-4 forms a non clathrin-associated coat on vesicles departing the trans-Golgi network (TGN) and may be involved in the targeting of proteins from the trans-Golgi network (TGN) to the endosomal-lysosomal system (PubMed:11139587, PubMed:20230749). It is also involved in protein sorting to the basolateral membrane in epithelial cells and the proper asymmetric localization of somatodendritic proteins in neurons (By similarity). Within AP-4, the mu-type subunit AP4M1 is directly involved in the recognition and binding of tyrosine-based sorting signals found in the cytoplasmic part of cargos (PubMed:10436028, PubMed:11139587, PubMed:20230749, PubMed:26544806). The adaptor protein complex 4 (AP-4) may also recognize other types of sorting signal (By similarity).
Involvement in disease
Spastic paraplegia 50, autosomal recessive
SPG50
A form of spastic paraplegia, a neurodegenerative disorder characterized by a slow, gradual, progressive weakness and spasticity of the lower limbs. Rate of progression and the severity of symptoms are quite variable. Initial symptoms may include difficulty with balance, weakness and stiffness in the legs, muscle spasms, and dragging the toes when walking. In some forms of the disorder, bladder symptoms (such as incontinence) may appear, or the weakness and stiffness may spread to other parts of the body. SPG50 affected individuals present postnatally with early infantile hypotonia, delayed psychomotor development, strabismus, lack of independent walking and severe intellectual disability. They develop progressive spasticity of all limbs with generalized hypertonia, hyperreflexia, and extensor plantar responses by the end of the first year of life. Speech is absent or limited. Pseudobulbar signs, such as drooling, stereotypic laughter, and exaggerated jaw jerk, are part of the clinical picture.
None
The disease is caused by variants affecting the gene represented in this entry.
Sequence Similarities
Belongs to the adaptor complexes medium subunit family.
Tissue Specificity
Ubiquitous. Highly expressed in testis and lowly expressed in brain and lung.
Cellular localization
- Golgi apparatus
- trans-Golgi network membrane
- Peripheral membrane protein
- Early endosome
- Found in soma and dendritic shafts of neuronal cells.
Alternative names
MUARP2, AP4M1, AP-4 complex subunit mu-1, AP-4 adaptor complex mu subunit, Adaptor-related protein complex 4 subunit mu-1, Mu subunit of AP-4, Mu-adaptin-related protein 2, Mu4-adaptin, mu-ARP2, mu4