Collagens

thumb|upright=1.5|The triple helix: three left-handed polyproline type II helices (red, green, blue) assemble by an axial hydrogen bond to form a right-handed triple helix, the tertiary structure of collagen.

Spongin, a modified type of collagen protein, forms the fibrous skeleton of most organisms among the phylum Porifera, the sponges. It is secreted by sponge cells known as spongocytes.

a collagen trimer containing alpha(I) chains

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

[[Image:endostatin.jpeg|thumb|right|Endostatin monomer, basic amino acid residues shown in red (source: pdb.org, 1KOE).]] Endostatin is a naturally occurring, 20-kDa C-terminal fragment derived from type XVIII collagen. It is reported to serve as an anti-angiogenic agent, similar to angiostatin and thrombospondin.

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

collagen homotrimer of alpha1(II) chains

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

Prolargin is a protein that in humans is encoded by the PRELP gene.

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens

mammalian protein found in Homo sapiens