Mu homology domain (MHD) of adaptor-like proteins (AP-like), stonins
A small family of proteins named stonins has been characterized as clathrin-dependent AP-2 mu2 chain related factors, which may act as cargo-specific sorting adaptors in endocytosis. Stonins include stonin 1 and stonin 2, which are only mammalian homologs of Drosophila stoned B, a presynaptic protein implicated in neurotransmission and synaptic vesicle (SV) recycling. They are conserved from C. elegans to humans, but are not found in prokaryotes or yeasts. This family corresponds to the mu homology domain of stonins, which is distantly related to the C-terminal domain of mu chains among AP complexes. Due to the low degree of sequence conservation of the corresponding binding site, the mu homology domain of stonins is unable to recognize tyrosine-based endocytic sorting signals. To data, little is known about the localization and function of stonin 1. Stonin 2, also known as stoned B, acts as an AP-2-dependent synaptotagmin-specific sorting adaptors for SV endocytosis. Stoned A is not a stonin. It is structurally unrelated to the adaptins and does not appear to have mammalian homologs. It is not included in this family.
Jiyao W et al.(2023). "The conserved domain database in 2023.",