The term collagens encompasses a broad array of proteins each possessing a ternary spiral. They are enormously abundant in the carnal land being the most abundant proteins in mammals accounting for 30 % of protein. To day of the month there are a lower limit of 29 genetically different members of the collagen household ( Carter and Raggio 2009 ) . These can be separated in to assorted subcategories including fibril forming collagens. Collagen type one is the most abundant member of this subfamily. These are exceptionally of import biomechanically ( Hulmes 2002 ) being present in about every structurally of import tissue and giving support to most variety meats. It does nevertheless hold other functions such as commanding cell activity and extracellular matrix ( ECM ) formation and debasement by moving as a ligand toward specific cell receptors ( Leitinger ) . Fibrilar collagens all have a similar primary construction which is indispensable for ternary spiral and fibril formation.
biogenesis
Collagen biogenesis is far from a straightforward procedure as it involves legion stairss above the usual written text interlingual rendition procedure required for the formation of a protein. The collagen molecule is formed from 3 alpha fractional monetary units. In collagen type 1 there are 2 alpha 1 -chains and 1 alpha 2 concatenation. Each of these alpha ironss is formed in to a left manus spiral, with 3 amino acids ( AAs ) per bend, and these are brought together organizing a right manus ace spiral. Each collagen molecule is comprised of a cardinal ternary coiling part, which accounts for around 95 % of the molecule. With a non coiling part at either terminal. These non coiling parts are known as telopeptides ( N-telopeptide at N-terminus and C-telopeptide at C-terminus ) . In order for the ternary coiling part to organize right a rigorous form of AAs must be followed with every 3rd AA being Glycine. this is due to the fact that in the Centre of the ternary spiral there is deficient infinite to suit side ironss larger than the individual H atom nowadays on Glycine. The form may be written ( Gly-X-Y ) N where N is the figure of repetitions. N may be between 337 and 343. Ten and Y are frequently proline and hydroxy-proline. It follows that as the little side concatenation of Glycine is required in the Centre of the ternary spiral the side ironss of proline and hydroxyproline are orientated towards the exterior of the molecule. Here they participate extensively in intermolecular and intramolecular interactions.
The alpha polypeptide ironss are synthesised as pre-procollagen on ribosomes of the unsmooth endoplasmic Reticulum ( rER ) of a cell ( most normally fibroblasts ) . Pre-procollagen has big N and C terminal globular spheres and a 23 AA long ( comparatively abruptly ) hydrophobic signal peptide which allows it to perforate the unsmooth endoplasmic Reticulum where it is removed by the signal protease enzyme. These are so joined at their several C-terminuses and the ternary spiral formation progresss towards the N-terminus resulting in a procollagen molecule. This procedure involves legion specialised enzymes and chaperones which are required to guarantee right folding and carry out concatenation association and stabilisation. ( Kivirikko and Myllyla ) . The ternary spiral is stabilised by H bonds which form between the NH of glycine and the back bone of the c=o bond of the residue in the ten place of the next concatenation. this causes a deficiency of rotary motion around the calpha-atom of proline taking to stabilization.
This procedure nevertheless can non happen before the polypeptide chains undergo legion station translational alterations ( PTMs ) . These alterations include the hydroxylation of proline and lysine residues to organize hydroxy-proline and hydroxy-lysine severally ; glycosylation ( N or O linked ) , disulphide adhering, isomerization, trimerisation and ternary spiral folding.
Procollagen molecules are so transported through the Golgi web being packed in to cysts ready for secernment into extracellular infinite. There is so cleavage of the propeptides from both the N and C end points. This cleavage is enzymatic and utilises a disintegrin and metalloproteinase with thrombospondin motives ( ADAMTS ) , tolloid-like proteases and bone morphogenetic protein 1 ( BMP1 ) . This gives rise to the mature signifier of the molecule.
The mature collagen type 1 molecules so pack together in a self-generated mode so that they are aligned in analogue. They are besides staggered giving rise to a banded construction giving rise to a banded visual aspect in microscopy. The sets are repeated every 67nm, this distance is known as D. The 300nm length of a collagen molecule can be written as 4.4D with 0.4D stand foring the overlap distance of the terminals. The filament is so stabilised by widespread intermolecular cross linking.
station translational alteration
intracellular
hydroxylation of lysine
Human type 1 collagen alpha1 concatenation contains 38 lysine residues: the coiling part incorporating 36 and each of the telopeptides incorporating 1. An alpha 2 concatenation contains 31: coiling part incorporating 30 and the n-telopeptide containing 1. It has been shown that the figure of lysine molecules hydroxylated within a collagen molecule is more varied than in proline. By and large there is systematically about 50 % hydroxylation of the proline residues irrespective of the type of collagen, the tissue in which it is present or the physiological conditions. on the other manus the figure of lysine residues hydroxylated varies significantly between collagens, between assorted tissues and even under different physiological conditions. ( Uzawa, Yeowell et al. )
ternary spiral formation
extracellular
cross-linking
Carter, E. M. and C. L. Raggio ( 2009 ) . “ Familial and orthopaedic facets of collagen upsets. ” Current Opinion in Pediatrics 21 ( 1 ) : 46-54.
Hulmes, D. J. S. ( 2002 ) . “ Building collagen molecules, filaments, and suprafibrillar constructions. ” Journal of Structural Biology 137 ( 1-2 ) : 2-10.
Kivirikko, K. I. and R. Myllyla “ Posttranslational enzymes in the biogenesis of collagen: intracellular enzymes. ” Methods in Enzymology 82 Pt A: 245-304.
Leitinger, B. “ Transmembrane collagen receptors. ” Annual Review of Cell & A ; Developmental Biology 27: 265-290.
Uzawa, K. , et Al. “ Lysine hydroxylation of collagen in a fibroblast cell civilization system. ” Biochemical & A ; Biophysical Research Communications 305 ( 3 ) : 484-487.
