AP4S1
# AP4S1

AP-4 complex subunit sigma-1 is a protein that in humans is encoded by the AP4S1 gene.

## Function

The heterotetrameric adaptor protein (AP) complexes sort integral membrane proteins at various stages of the endocytic and secretory pathways. AP4 is composed of 2 large chains, beta-4 (AP4B1) and epsilon-4 (AP4E1), a medium chain, mu-4 (AP4M1), and a small chain, sigma-4 (AP4S1, this gene).

## Clinical relevance

Deficiency of AP-4 leads to childhood-onset hereditary spastic paraplegia and it is currently hypothesized that AP4-complex-mediated trafficking plays a crucial role in brain development and functioning.

