3.A.34. The Sorting Nexins of the ESCRT Complexes (SN-ESCRT)
Sorting nexins are numerous; in humans there are 33 protein constituents that have been considered to be constituents of ESCRT complexes to date (7/2023) (Weeratunga et al. 2020). These proteins are SNX1 - 27 and SNX29 - 33. The UniProt proteins are listed here. SNX28 is called the NADPH oxidase organizer 1 and has the UniProt acc # Q8VCM2. It may or may not be involved in the functioning of an ESCRT complex. Twenty of these sorting nexins show at least some degree of sequence similarity and therefore can be considered to be paralogs. They presumably function in overlapping capacities (Chen et al. 2019).
Recycling of membrane proteins enables the reuse of receptors, ion channels and transporters. A key component of the recycling machinery is the endosomal sorting complex for promoting exit 1 (ESCPE-1), which rescues transmembrane proteins from the endolysosomal pathway for transport to the trans-Golgi network and the plasma membrane. This rescue entails the formation of recycling tubules through ESCPE-1 recruitment, cargo capture, coat assembly and membrane sculpting. ESCPE-1 has a single-layer coat organization, suggesting how synergistic interactions between ESCPE-1 protomers, phosphoinositides and cargo molecules result in an arrangement of amphipathic helices to drive tubule formation. This defines a key process of tubule-based endosomal sorting (Lopez-Robles et al. 2023).