Identification and characterization of type II collagen mutations

Abstract

Collagen type II is a prototypic fibrillar collagen. It is the main structural protein of articular cartilage and the cartilaginous enlage of endochondral bone development. One way to study the normal structure and function of type II collagen is to study the structure of abnormal type II collagen in inherited diseases of the skeleton.Within the skeletal dysplasias a small subset of chondrodysplasias are emerging that are produced by mutations in the gene for type II collagen, COL2A1. This dissertation presents thru protein biochemistry the identification and characterization of structurally defective type II collagen in cases of hypochondrogenesis, spondyloepimetaphyseal dysplasia (SEMD), and Kniest dysplasia.In a perinatal lethal form of hypochondrogenesis a glutamate for glycine(853) substitution was identified. In the SEMD case a serine for glycine(841) was identified. And in two unrelated probands with Kniest dysplasia a deletion of a seven amino acids(102--108) was identified.The type II collagen from the cartilage of these affected probands and from additional cases of hypochondrogenesis and premature osteoarthritis were post-translationally overmodified. Amino acid sequencing of specific lysines revealed that the overmodification occurred primarily amino terminal to the mutation site and the degree of overmodification was proportional to the severity of the disease phenotype. The exception was the two Kniest dysplasia probands. The seven amino acid deletion was unique for it disrupted the Gly-x-y repeat of the triple helix. Type II collagen from these probands was overmodified amino and carboxy terminal to the mutation site.