5.16.2.2.3 (*3*) III collagen
(*3*) III collagen belongs to the fibrillar collagen group. Its molecular construction is much like that of kind I collagen. The molecule is a homotrimer with the chain composition of (*1*) 3 . The main tissue localization of kind III collagen is in dermis and aorta. In tendon and bone, the ratio of kind III collagen to kind I collagen could be very low. Latest research have proven that kind III collagen represents nearly 10% of the whole collagen elements in cartilage.32 (*3*) II and III collagens exist in single fibrils.107 A number of the kind III collagen molecules are cross-linked with kind II collagen.32 (*3*) III procollagen (pN-type III collagen) will be purified from tissue for biophysical evaluation. (*3*) III collagen incorporates distinctive covalent cross-links at each the N- and C-terminal ends adjoining to the triple helical area and is an effective supply for refolding experiments.105 The C-terminal finish of the foremost collagenous area has the sequence -GPPGAPGPCCG-. The six cysteine residues from the three chains type three pairs of disulfide bonds (see Part 5.16.4.1.1). Additionally, the foremost triple helical area, 1029 residues in people, is a little bit longer than the identical area in kind I and II collagen molecules containing 1014 residues. (*3*) III collagen is synthesized as procollagen III in an analogous method to kind I collagen. Nevertheless, whereas many of the N-propeptide of the procollagen kind I molecule is cleaved and tough to extract from tissue, the pN-type III collagen is processed partially,109,110 and is thought to be deposited within the pores and skin at vital ranges.111 Immunoelectron histochemistry utilizing a monoclonal antibody made in opposition to the triple helical area recommended that kind III collagen is localized in pores and skin collagen fibrils no matter fibril diameter.112,113 The sort III collagen null mouse58 was proven to have ruptures in main blood vessels, indicating that this molecule is important for the structural integrity of the circulatory system. Nevertheless, the molecular operate of kind III collagen and pN-type III collagen continues to be utterly unknown. The tyrosine residues in a pepsin-susceptible area of kind III collagen are sulfated by tyrosylprotein sulfotransferase (TPST, EC 2.8.2.20).114 This modification was proven to happen within the trans-Golgi throughout secretion of the procollagen molecule.115 The organic position of sulfation could be associated to development regulation of the collagen fibrils though particulars of this mechanism are unknown.116
A sequence of brief peptide fragments of kind III collagen have been used to seek out binding websites with different molecules. DDR-2 has been proven to work together with a sort III collagen mannequin peptide with the minimal sequence of GVMGFO (the place O is 4-hydroxyproline).117 It’s fascinating to notice that this identical sequence can be concerned with the collagen interplay of SPARC.118
Greater than 100 mutations of the COL3A1 gene may cause Ehlers–Danlos syndrome (EDS) kind IV, an autosomal dominant dysfunction characterised by joint and dermal manifestations much like the opposite types of the syndrome, however as well as these people are vulnerable to spontaneous ruptures of bowel and enormous arteries.