Table 1.

Types of fibrillar collagens and their basic functions and occurrence in the body [23,25,31].

Type	Structure	Localization	Function
I	Triple superhelix composed of two identical α1 and one α2 chain; a form consisting of three α1 chains (homotrimeric) is also found	Bones, tendons, ligaments, skin, cornea	Tensile strength of tissues and bone stiffness
II	Three identical α1[III]3 chains—homotrimer; similar properties and size to type I, but higher content of hydroxylysine and glucose and galactose residues	The dominant component of vitreous tissue (approx. 80%), corneal epithelium, and cartilage	One of the main components of ECM (extracellular matrix), maintains chondrocyte functions, induces cell adhesion and proliferation
III	Three identical α1[III]3 chains	Element of the dermis, liver and lung tissues, spleen and blood vessels	Gives elasticity to tissues
V	Three different chains—heterotrimers	Bones, skin, placenta, cornea	Initiation of collagen fibrillogenesis
XI	Three different chains—heterotrimers	Cartilage, intervertebral discs	Initiation of collagen fibrillogenesis
XXIV	The fragment of the Gly-Xaa-Yaa repeated sequence is relatively short, constitutes approximal	Bones, cornea	A marker of osteoblast differentiation and bone formation in mice
XXVII	Forms non-striated, thread-like structures, unlike other members of the subfamily	Cartilage	Deposited mainly in skeletal tissues at the junction of cartilage and bone