Matrix fully loaded: Assembly and secretion of collagen fibrils

The secretory pathway operates like a well-oiled machine when it comes to secreting small proteins. But how does it cope with stiff rod-like molecules such as type I collagen, which spontaneously self-assembles into the millimetre-long collagen fibrils that are characteristic of the extracellular matrix (ECM)? A recent study in our laboratory shows that the secretory pathway adapts exquisitely to intracellular fibril formation by creating tubular vesicles that dock to specialized secretory nozzles in the plasma membrane (E.G. Canty, Y. Lu, R.M. Meadows, M. Shaw, D.F. Holmes and K.E. Kadler, unpublished work). This article gives a brief account of the biochemical and structural work that led up to these new observations.