Hydroxylysine residues are glycosylated. N-linked sugars are added to the terminal portion of the polypeptide. Polypeptide chains form a triple helix molecule. Procollagen is formed through intrachain and interchain disulfide bonds which stabilise the polypeptides and determine the shape of the molecule. Procollagen is packed into secretory granules which move along microtubules to be released into the extracellular matrix Extracellular Events Uncoiled terminal ends of procollagen are cleaved to form tropocollagen.
Fibrils aggregate to form collagen fibres.
Collagen catabolism is poorly understood, but enzymatic processes and mechanical factors may be involved. The process of proteoglycan synthesis begins with translation of mRNA to form a protein core to which glycosaminoglycan chains are added. The resultant aggrecan molecules are transported to secretory vesicles and released into the extracellular matrix. Link proteins and hyaluronate from the cell membrane bind to the molecules forming proteoglycan aggregates. Proteoglycan catabolism depends on cleavage of globular domains resulting in non-aggregation of the resultant fragments.