n. (context biology English) An assembly of protein in a plasma membrane at which endocytosis occurs
Eisosomes ('eis' meaning into or portal and 'soma', meaning body) are large, heterodimeric, immobile protein complexes at the plasma membrane which mark the site of endocytosis in some eukaryotes, and were discovered in the yeast Saccharomyces cerevisiae in 2006. Currently, seven genes: Pil1, Lsp1 and Sur7, Eis1, Seg1 and Ygr130C, Seg2, are annotated to the formation of the proteins identified in eisosomes. These organelle-like structures have put to rest the idea that sites of endocytosis in cells are chosen at random. Eisosomes have a profound role in regulating plasma membrane architecture and organization in yeast. Microscopic and genetic analyses link these stable, ultrastructural assemblies to the endocytosis of both lipid and protein cargoes in cells.
There are approximately 50–100 eisosomes in each mature yeast cell distributed uniformly across the cell surface periphery in a characteristic dotted pattern with each eisosome containing approximately 2000–5000 copies of Pil1 and Lsp1 proteins, as well as, integral membrane protein Sur7. Only a few of the eisosomes present in a cell are active at any one time, suggesting that eisosomes function by using reversible phosphorylation and are regulated portals that govern both location and magnitude of membrane traffic into the cell.