Collagen: molecular diversity in the body's protein scaffold.

Intensive research in the last decade has revealed a wealth of detail on the mechanism of biosynthesis, molecular structure, and covalent cross-linking of collagen. Tissues of higher animals express a family of at least five genetically distinct types of collagen molecule, each apparently tailored for different construction work outside the cell. Within each genetic type of collagen, further chemical heterogeneity is also evident; the variations in hydroxylation, glycosylation, and cross-linking are dependent, for example, on tissue type, age, and hormonal status. The functional significance of collagen's molecular diversity and its control by different cells and tissues are not yet well understood but abnormalities of collagen in many human diseases keep this protein a focal molecule of medical research.