Transport of lysosomal membrane proteins from the Golgi complex to lysosomes

Abstract

Lysosomes are intracellular organelles with an acid interior (pH <5) bounded by a single membrane and containing many lysosomal hydrolases that are optimally active at an acid pH (Kornfeld and Mellman 1989). Lysosomes are mannose 6-phosphate receptor (MPR) negative and devoid of labeling for phosphorylated lysosomal enzymes, but positive for fluid phase en-docytic markers if they are internalized for a long (>4h) time (Ludwig et al. 1991). The lysosomal limiting membrane contains a high concentration of integral membrane proteins including the lysosome-associated membrane protein 1 (LAMP-1), LAMP-2, and lysosomal integral membrane proteins 1 and 2 (LIMP-1/CD63 and LIMP-2) (Eskelinen et al. 2003). Mature lysosomes may occasionally contain a clathrin coat (Traub et al. 1996).