Amino Acids, Proteins and Porphyrins
Triple helix is found in
1. Extra cellular matrix contains 3-major class of Biomolecules
a. Structural proteins — collagen and Elastin
b. Specialized proteins: - Fibrillin, fibronectin and Laminin
a. Most abundant protein in animal word, constitutes about 25% of the protein in mammals
b. About 19 distinct types of collagen, are identified in human tissue.
c. All collagen types have a Triple helical structure.
d. A striking characteristic of collagen is the occurrence of glycine residues on every third position ie.
(gly-x-y-gly-x-y….. ) n. About 100 of x-position are proline and about 100 of Y-position are
e. Post translational Hydroxylation of proline→Hydroxyproline by Prolyl Hydroxylase, whose co-
factors are vit. C and α-Ketoglutarate which are also cofactors for lysyl hydroxylase (converts lysine →hydroxylysine).
3. Glycosylation of Hydroxylysine→through an 0-Glucosidic linkage, unique to collagen.
f. 6. Collagens are further stabilized by the formation of covalent cross-links mediated by Lysyl oxidase
(a copper dependent enzyme)
g. 7. Abnormities of collagen synthesis eg.
A. Osteogenesisimperfecta→abnormalities in gene coding for pro-collagen α-1 (i.e. Type I- collagen)
B. Ehlers’ Danlos-syndrome (EDS) -
Type IV EDS: - Most serious vascular type - due to abnormalities in type III collagen. (Autosomal dominant)
Type VI EDS: - Due to deficiency of Lysyl Hydroxylase.
Type VII, C; EDS → Deficiency of pro-collagen-N-Proteinase.
C. Menkes’s disease: - Abnormal copper transport due to mutation in ATP7A gene C/B →
kinky hair, Growth retardation.
D. Alport’s syndrome: - Due to mutation in genes encoding Type IV collagen.
E. EpidermolysisBullosa: - Due to mutation in COL7A1 affecting the structure of type VII collagen
Epidermolysisbullosa simplex - Due to mutation in Keratin 5
DNA →is Double helix structure.