Figure 4.

Secretion of fibrils to ECM in tenoblasts. A. The collagen gene expression and assembly of triple helix occurs in the ER lumen of tenoblasts. The procollagen is then processed in Golgi apparatus and is transported to plasma membrane for exocytosis of mature collagen to ECM where the fibril formation takes place. B. The molecular events in the assembly of fibril. The procollagen type I subunits were synthesized in the ER lumen which align to form triple helix by nucleating at the C terminal end by disulphide formation. The collagen triple helix matures by the trimming of PICP and PINP by corresponding proteases. This triple helix aligns at end-to-end fashion in the ECM to form fibrils.