Three identical type III procollagen chains come together at the carboxy-terminal ends, and the structure is stabilized by the formation of disulphide bonds.

The large globular domains from both ends of the molecule are removed by C- and amino(N)-terminal-proteinases to generate triple-helical type III collagen monomers called tropocollagen.

The periodicity induced by the glycines at non-integer spacing results in a super-helix that completes one turn in about 20 amino acids.

Type III collagen is found as a major structural component in hollow organs such as large blood vessels, uterus and bowel.

[9][10][11] The resulting defective protein is the cause of a severe, rare disease, the vascular type of Ehlers-Danlos syndrome (vEDS).

It is the most severe form of EDS, since patients often die suddenly due to rupture of large arteries or other hollow organs.

[11][9] Interestingly, most of these mutations lead to exon skipping, and produce a shorter polypeptide, in which the Gly-Xaa-Yaa triplets stay in frame and there are no premature termination codons.

In other words, the collagens can be subjected to a short digestion by proteinases called trypsin and chymotrypsin at increasing temperatures.

[12][24] This refers to a situation where one of the parents carries the mutation in some, but not all of her or his cells, and appears phenotypically healthy, but has more than one affected offspring.

Increased amounts of type III collagen are found in many fibrotic conditions such as liver and kidney fibrosis, and systemic sclerosis.

[33][34][35][36] Inactivation of the murine COL3A1 gene using homologous recombination technique led to a shorter life span in homozygous mutant mice.

These mice developed severe skin wounds, demonstrated vascular fragility in the form of reduced tensile strength and died prematurely at the age of 13–14 weeks.