The Alteromonas phage P24 Coat Protein (P24CP) Family
Coat protein (COP) I and COP II complexes are involved in the transport of proteins between the endoplasmic reticulum and the Golgi apparatus in eukaryotic cells. The formation of COP I/II complexes at membrane surfaces is an early step in vesicle formation and is mastered by p24, a type I transmembrane protein. Oligomerization of p24 monomers may to be mediated and/or stabilized by interactions within the transmembrane domain, and the single p24 TMS appears to selectively bind a single sphingomyelin C18:0 molecule. Pannwitt et al. 2019 showed that sequence-specific dimerization of the p24 TMS is mediated by an LQ7 motif, with Gln(187) being of special importance. Whereas cholesterol has no direct impact on p24 dimerization, binding of a sphingolipid can control dimerization of p24 in rigid membrane regions. The authors suggest that specific binding of a sphingolipid to the p24 transmembrane helix affects p24 dimerization in membranes. A clearly defined p24 dimerization propensity is crucial for p24 activity, which involves shuttling between the endoplasmic reticulum and the Golgi membrane, in which cholesterol and sphingolipid C18:0 concentrations differ (Pannwitt et al. 2019).