Role of cartilage-associated protein in skeletal development.

The past 3 years have been exciting for collagen biologists and human geneticists studying the disease known as osteogenesis imperfecta (OI or brittle bone disease). Functional studies on cartilage-associated protein (Crtap) have identified it as an essential component of a heterotrimeric, endoplasmic reticulum resident complex responsible for collagen prolyl 3-hydroxylation and chaperone function. Importantly, human mutations in the CRTAP gene have been associated with recessive forms of OI. Although the function and in vivo biological significance of the 3-hydroxyproline modification are still poorly understood, studies on Crtap have led to the identification of additional genes in which mutations also cause recessive forms of OI. These discoveries have now focused the interest of geneticists on the endoplasmic reticulum that will require the help of biochemists to unravel the molecular dynamics and complexities of collagen folding.