Molecular organization, structural features, and ligand binding characteristics of CD44, a highly variable cell surface glycoprotein with multiple functions

CD44 is a type I transmembrane protein and member of the cartilage link pro tein family. It is involved in cell-cell and cell-matrix interactions and s ignal transduction. Several CD44 ligands have been identified. CD44 is a ma jor cell surface receptor for hyaluronan, a component of the extracellular matrix. It is implicated in diseases such as cancer and inflammation and th erefore intensely studied. A characteristic feature of CD44 is the occurren ce of many isoforms that are expressed in a cell-specific manner and differ entially glycosylated. Although a number of CD44 isoforms have been charact erized, the structural diversity of CD44 makes it often challenging to stud y (isoform-specific) CD44-ligand interactions at the molecular level of det ail. The structural organization and ligand binding characteristics of CD44 are focal points of this review. On the basis of recent structural and mut agenesis studies, details of the CD44-hyaluronan interaction are beginning to be understood. Proteins 2000;39:103-111. (C) 2000 Wiley-Liss, Inc.