Transmembrane domain mutations influence the cellular distribution of lysosomal membrane glycoprotein A.

The Igp/LAMP family of mammalian and avian lysosomal type I membrane glycoproteins features short, conserved, cytosolic tails that possess lysosomal targeting information. The sequences of the adjacent transmembrane domains are also highly conserved, with six amino acids identical in all sixteen known Igp variants. These six residues are found along one side of a hypothetical alpha-helix that may comprise this domain. We substituted or deleted some of the conserved transmembrane residues in mouse Igp-A and stably expressed the proteins in Chinese hamster ovary cells. We examined various properties and transport characteristics of the normal and modified proteins and concluded that the transmembrane domain serves as more than just a membrane anchor, as it subtly influences the cellular distribution of the protein as well.