CD107a, also known as lysosomal-associated membrane protein 1 (LAMP-1), is a heavily glycosylated type I transmembrane protein that constitutes one of the two major sialoglycoproteins on lysosomal membranes that can be used to distinguish lysosomes from other organelles. It is a ligand for galaptin, an S-type lectin present in extracellular matrix, through its recognition of acetyllactosamine oligosaccharide chains and is a ligand for E-selectin-mediated cell adhesion. CD107a is principally expressed in epithelial cells and macrophages in a variety of organs in normal and beige mutant mice. It may function in protecting the inner surface of the lysosomal membrane by forming a barrier to lysosomal hydrolases.