C-terminal domain of medium Mu1 subunit in clathrin-associated adaptor protein (AP) complex AP-1
AP complexes participate in the formation of intracellular coated transport vesicles and select cargo molecules for incorporation into the coated vesicles in the late secretory and endocytic pathways. There are four AP complexes, AP-1, AP-2, AP-3, and AP-4, described in various eukaryotic organisms. Each AP complex consists of four subunits: two large chains (one each of gamma/alpha/delta/epsilon and beta1-4, respectively), a medium mu chain (mu1-4), and a small sigma chain (sigma1-4). Each of the four subunits from the different AP complexes exhibits similarity with each other. This family corresponds to the C-terminal domain of heterotetrameric clathrin-associated adaptor protein complex 1 (AP-1) medium mu1 subunit, which includes two closely related homologs, mu1A (encoded by ap1m1) and mu1B (encoded by ap1m2). Mu1A is ubiquitously expressed, but mu1B is expressed exclusively in polarized epithelial cells. AP-1 has been implicated in bi-directional transport between the trans-Golgi network (TGN) and endosomes. It plays an essential role in the formation of clathrin-coated vesicles (CCVs) from the trans-Golgi network (TGN). Epithelial cell-specific AP-1 is also involved in sorting to the basolateral surface of polarized epithelial cells. Recruitment of AP-1 to the TGN membrane is regulated by a small GTPase, ADP-ribosylation factor 1 (ARF1). Phosphorylation/dephosphorylation events can also regulate the function of AP-1. The membrane-anchored cargo molecules can be linked to the outer lattice of CCVs by AP-1. Those cargo molecules interact with adaptors through short sorting signals in their cytosolic segments. Tyrosine-based endocytotic signals are one of the most important sorting signals. They are of the form Y-X-X-Phi, where Y is tyrosine, X is any amino acid and Phi is a bulky hydrophobic residue that can be Leu, Ile, Met, Phe, or Val. These kinds of sorting signals can be recognized by the C-terminal domain of AP-1 mu1 subunit, also known as Y-X-X-Phi signal-binding domain that contains two hydrophobic pockets, one for the tyrosine-binding and one for the bulky hydrophobic residue-binding.
Feature 1:signal peptide binding site [polypeptide binding site]
Evidence:
Comment:Based on structure that shows that human mu2 adaptin subunit of AP-2 adaptor binds signal peptides.
Comment:C-terminal domain of heterotetrameric adaptor protein (AP) complexes medium mu subunits binds Y-X-X-Phi-type tyrosine-based signals, where Y is tyrosine, X is any amino acid and Phi is a bulky hydrophobic residue that can be Leu, Ile, Met, Phe, or Val.
Jiyao W et al.(2023). "The conserved domain database in 2023.",