Fibrillar collagen is synthesized in the ER as procollagen with N- and C-terminal propeptides flanking the collagenous domain (Bellamy & Bornstein 1971). These propeptides, particularly the C-propeptide, inhibit fibril formation (Kadler et al. 1987). Type V collagen N-propeptide removal is partial, and reported to be mediated by BMP-1 which cleaves between the proline/arginine-rich protein domain and the variable domain of the alpha1 chain and between the small and the large collagenous domain of alpha3 chain (refs. in Colige et al. 2005). Mutations in procollagen peptide type V (COL5A1) can cause diseases such as Ehlers-Danlos Sydrome. Majority of the cases result from haploinsufficiency of COL5A1 protein that may lead to a disorganised extracellular matrix. Moreover, other mutations result in structural defects which may in turn result in defective collagen fibrils. The accumulation and interaction of this defective collagen fibrils may lead to ER stress and other complications in the cell (Takahara K et al. 2002, Symoens S et al. 2012).