Proposed since September 2017.
Tropocollagen molecule: three left-handed procollagens (red, green, blue) join to form a right-handed triple helical tropocollagen.
Collagen /ˈkɒlədʒɪn/ is the main structural protein in the extracellular space in the various connective tissues in animal bodies. As the main component of connective tissue, it is the most abundant protein in mammals,  making up from 25% to 35% of the whole-body protein content. Collagen consists of amino acids wound together to form triple- helices to form of elongated fibrils .  It is mostly found in fibrous tissues such as tendons , ligaments and skin .