5.16.2.2.3 (*3*) III collagen
(*3*) III collagen belongs to the fibrillar collagen group. Its molecular construction is just like that of sort I collagen. The molecule is a homotrimer with the chain composition of (*1*) 3 . The key tissue localization of sort III collagen is in dermis and aorta. In tendon and bone, the ratio of sort III collagen to sort I collagen may be very low. Latest research have proven that sort III collagen represents nearly 10% of the entire collagen elements in cartilage.32 (*3*) II and III collagens exist in single fibrils.107 A few of the sort III collagen molecules are cross-linked with sort II collagen.32 (*3*) III procollagen (pN-type III collagen) might be purified from tissue for biophysical evaluation. (*3*) III collagen accommodates 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 most important collagenous area has the sequence -GPPGAPGPCCG-. The six cysteine residues from the three chains kind three pairs of disulfide bonds (see Part 5.16.4.1.1). Additionally, the most important triple helical area, 1029 residues in people, is a bit longer than the identical area in sort I and II collagen molecules containing 1014 residues. (*3*) III collagen is synthesized as procollagen III in an analogous method to sort I collagen. Nevertheless, whereas many of the N-propeptide of the procollagen sort 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 towards the triple helical area recommended that sort III collagen is localized in pores and skin collagen fibrils no matter fibril diameter.112,113 The kind III collagen null mouse58 was proven to have ruptures in main blood vessels, indicating that this molecule is crucial for the structural integrity of the circulatory system. Nevertheless, the molecular perform of sort III collagen and pN-type III collagen remains to be utterly unknown. The tyrosine residues in a pepsin-susceptible area of sort 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 function of sulfation is likely to be associated to progress regulation of the collagen fibrils though particulars of this mechanism are unknown.116
A collection of quick peptide fragments of sort III collagen have been used to search 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 attention-grabbing to notice that this identical sequence can also be concerned with the collagen interplay of SPARC.118
Greater than 100 mutations of the COL3A1 gene could cause Ehlers–Danlos syndrome (EDS) sort IV, an autosomal dominant dysfunction characterised by joint and dermal manifestations just like the opposite types of the syndrome, however as well as these people are susceptible to spontaneous ruptures of bowel and huge arteries.