Type I collagen synthesis in the context of Osteogenesis imperfecta (Homo sapiens)

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21, 3-5Collagen synthesisalpha1 chain withchaperonesGolgi apparatusnecessary for intracellularcalcium flux and involvedin cell differentiationCytoplasmUnknown crucial role during bone mineralization,hypothesized interactionwith PEDF (SERPINH1)Triple helixMature type I collagenStabilised fibrilsAlpha chains combined to form triple helixCleavage of propeptides of procollagen modified alpha2 chainRegulatoryProteinsModified alpha1 chainStabilisedtriple helixDifferentiation to osteoclastsOsteoblast differentiation(bone formation)osteoblast-specific transcriptionfactor essential for bone developmentRough endoplasmic reticulumRegulatory proteinstransported from ER membranein times of ER stressMIA3IFITM5P4HA1BMP1TNFRSF11AP4HA2LRP6SERPINH1FKBP10PLOD1PLOD2CRTAPTMEM38BCOL1A1TNFRSF11BCa2+SP7MBTPS1LRP5COLGALT1ADAMTS2COL1A2WNT1ITPR1SERPINF1P3H1MBTPS2PPIBP3H1TNFSF11CREB3L1P4HBLOXSERPINH1FZD1K+Triple helixCOL1A1Triple helixExtracellular spacealpha1 chain withchaperonesCa2+K+OMIM:225400Ehlers-Danlos syndrome,kyphoscoliotic type, 1OMIM:112240Cole-Carpenter syndrome 1OMIM:609220Bruck syndrome 2OMIM:259440Osteogenesis imperfecta, type IXOMIM:610682Osteogenesis imperfecta, type VIIOMIM:614856Osteogenesis imperfecta, type XIIIOMIM:616229Osteogenesis imperfecta, type XVIOMIM:301014Osteogenesis imperfecta, type XIXOMIM:259710Osteopetrosis,autosomal recessive 2OMIM:166210Osteogenesis imperfecta, type IIOMIM:259420Osteogenesis imperfecta, type IIIOMIM:166220Osteogenesis imperfecta, type IVOMIM:166200Osteogenesis imperfecta, type IOMIM:166210Osteogenesis imperfecta, type IIOMIM:259420Osteogenesis imperfecta, type IIIOMIM:166220Osteogenesis imperfecta, type IVOMIM:114000Caffey diseaseOMIM:613848Osteogenesis imperfecta, type XOMIM:613848Osteogenesis imperfecta, type XOMIM:610968Osteogenesis imperfecta, type XIOMIM:259450Bruck syndrome 1OMIM:610967Osteogenesis imperfecta, type VOMIM:613849Osteogenesis imperfecta, type XIIOMIM:615220Osteogenesis imperfecta, type XVOMIM:174810Familial Expansile OsteolysisOMIM:166710OsteoporosisOMIM:612301Osteopetrosis, Autosomal Recessive 7OMIM:144750Endosteal Hyperostosis, Autosomal DominantOMIM:224300DysosteosclerosisOMIM:259770Osteoporosis-Pseudoglioma SyndromeOMIM:615066Osteogenesis Imperfecta, Type XIVP3H2OMIM:239000Paget disease of bone 5, juvenile-onsetOMIM:610915Osteogenesis imperfecta, type VIIIOMIM:613982Osteogenesis imperfecta, type VI


Type I collagen — the major protein component of the extracellular matrix in bone, skin and tendon — is mainly secreted by osteoblasts, dermal fibroblasts and tenocytes. Despite the relatively simple structure of the collagen triple helix, the biosynthesis of type I procollagen is extremely complex, involving multiple steps and requiring an ensemble of proteins for post-translational modifications, folding, transport, secretion and quality control. The COL1A1 and COL1A2 transcripts are translated in the rough endoplasmic reticulum (rER), and the α(I)‑chains undergo a series of post-translational modifications. Helical prolines in position Y of the Gly-Xaa-Yaa repeat are hydroxylated in position C4 by prolyl 4‑hydroxylase 1 (P4H1), whereas specific prolines in the X positions are 3‑hydroxylated by P3H1 and P3H2. Some lysine residues are hydroxylated by lysyl hydroxylases (LH1 and LH2, encoded by PLOD1 and PLOD2 respectively), and glycosylation of hydroxylysines into galactosyl-hydroxylysine and glucosyl-galactosyl-hydroxylysine is catalysed by procollagen galactosyltransferase 1 and procollagen glucosyltransferase 1. After synthesis of the carboxy-terminal propeptide, it forms intra-chain disulfide bonds and remains attached to the rER membrane. Selection and association of the correct chains into a triple helix occur by diffusion of the C-propeptides attached to the rER membrane. A nucleus for triple helix formation is formed that staggers the chains in the correct order and initiates triple helix formation. Protein disulfide isomerase catalyses inter-chain disulfide bond formation, which stabilize the folding nucleus. Hydroxylation of proline residues and some lysine residues continues and triple helix formation proceeds from the C-terminal end towards the amino-terminal end. During this phase, 65 kDa FK506‑binding protein (FKBP65; encoded by FKBP10) and a complex formed by P3H1 — CRTAP– PPIase B (peptidyl-prolyl cis–trans isomerase B) — seem to play a crucial part. The complex is involved in the Hydroxylation of proline 986 of the collagen α1(I)-chain and α1(II)-chain and proline 707 of the α2(I)-chain, which are thought to be important for supramolecular assembly of collagen fibrils and to serve as binding sites for chaperones or small leucine-rich proteoglycans. Beyond its prolyl 3‑hydroxylase activity, the complex functions as a PPIase and chaperone for collagen folding. Indeed, the fast propagation of the triple helix requires the isomerization of cis peptide bonds that convert proline residues into trans configuration, mainly by PPIase B24. When most of the helix is folded, the N-propeptides associate and form the small triple helix within this domain. The newly formed triple helix is stabilized by serpin H1 (also known as HSP47; encoded by SERPINH1) and FKBP65. Further modifications occur during transport from the rER to the Golgi apparatus in special coat protein complex vesicles that contain melanoma inhibitory activity protein 3 (also known as TANGO1, encoded by MIA) and through the Golgi stack by cisternal maturation. Serpin H1 also has binding sites along the helical portion of the molecule and assists shuttling of folded collagen into the cis-Golgi. These biosynthetic steps depend on a proper rER environment (for example, optimal calcium levels and redox potential), and the quality-control mechanisms can lead to the activation of the unfolded protein response using the ER-associated degradation pathway or the autophagy-mediated lysosomal degradation system to eliminate molecules that were not properly folded. Once secreted, the propeptides of procollagen are cleaved by a disintegrin and metalloproteinase with thrombospondin motifs 2 (ADAMTS2) and bone morphogenetic protein 1 (BMP1) into mature type I collagen. This initiates collagen fibre formation and these fibrils are stabilized by crosslink formation, in which certain lysine and hydroxylysine residues in the triple helix and the telopeptides are oxidized by lysyl oxidases and converted into allysine and hydroxyallysine. These residues then initially form divalent crosslinks that convert into mature trivalent pyridinoline and pyrrole crosslinks to stabilize the fibril structure in tissues.

Bone formation consists of the secretion of bone extracellular matrix components (mainly type I collagen) by osteoblasts. The unmineralized bone matrix (osteoid) subsequently becomes mineralized. In addition, osteoblasts and osteocytes release many cytokines, including receptor activator of nuclear factor-κB ligand (RANKL; also known as TNFSF11) and osteoprotegerin (OPG, encoded by TNFRSF11B), which regulate bone resorption by osteoclasts. RANKL acts on osteoclast precursor cells by binding to receptor activator of nuclear factor-κB (RANK; also known as TNFRSF11A) on their surface, thereby favouring their differentiation to osteoclasts. OPG, by interacting with RANKL, prevents the binding of RANKL to RANK. Some osteoblasts become embedded in the mineralized bone matrix and differentiate to osteocytes, which produce, among other factors, sclerostin, an inhibitor of the WNT pathway that is known to stimulate bone formation by stimulating osteoblast activity.

Linked with a dotted arrow to the GeneProduct nodes are diseases caused by mutation in the respective gene.

Adapted from [5]

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  1. Morello R, Bertin TK, Chen Y, Hicks J, Tonachini L, Monticone M, Castagnola P, Rauch F, Glorieux FH, Vranka J, Bächinger HP, Pace JM, Schwarze U, Byers PH, Weis M, Fernandes RJ, Eyre DR, Yao Z, Boyce BF, Lee B; ''CRTAP is required for prolyl 3- hydroxylation and mutations cause recessive osteogenesis imperfecta.''; Cell, 2006 PubMed Europe PMC Scholia
  2. Marini JC, Forlino A, Bächinger HP, Bishop NJ, Byers PH, Paepe A, Fassier F, Fratzl-Zelman N, Kozloff KM, Krakow D, Montpetit K, Semler O; ''Osteogenesis imperfecta.''; Nat Rev Dis Primers, 2017 PubMed Europe PMC Scholia
  3. Forlino A, Cabral WA, Barnes AM, Marini JC; ''New perspectives on osteogenesis imperfecta.''; Nat Rev Endocrinol, 2011 PubMed Europe PMC Scholia
  4. Weis MA, Hudson DM, Kim L, Scott M, Wu JJ, Eyre DR; ''Location of 3-hydroxyproline residues in collagen types I, II, III, and V/XI implies a role in fibril supramolecular assembly.''; J Biol Chem, 2010 PubMed Europe PMC Scholia
  5. Vranka JA, Sakai LY, Bächinger HP; ''Prolyl 3-hydroxylase 1, enzyme characterization and identification of a novel family of enzymes.''; J Biol Chem, 2004 PubMed Europe PMC Scholia


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110981view14:41, 25 June 2020EgonwReplaced another two mim-conversion by mim-translocation
110651view10:13, 25 May 2020RleeFixed an unconnected line.
110645view10:03, 24 May 2020Azanklfixed some errors
110642view06:22, 24 May 2020AzanklModified description
110260view15:25, 30 April 2020EgonwReplaced secondary ChEBI identifiers with a primary identifiers.
109333view23:34, 13 March 2020KhanspersOntology Term : 'osteogenesis imperfecta' added !
108833view00:44, 1 February 2020RleeModified description
108832view00:42, 1 February 2020RleeModified description
108829view21:54, 31 January 2020KhanspersModified description
108815view03:02, 31 January 2020RleeModified description
108814view03:02, 31 January 2020RleeModified description
108813view03:01, 31 January 2020RleeModified description
108812view03:00, 31 January 2020RleeModified description
108811view02:56, 31 January 2020RleeModified description
108810view02:53, 31 January 2020RleeNew pathway

External references


View all...
NameTypeDatabase referenceComment
ADAMTS2GeneProductENSG00000087116 (Ensembl)
BMP1GeneProductENSG00000168487 (Ensembl)
COL1A1GeneProductENSG00000108821 (Ensembl)
COL1A2GeneProductENSG00000164692 (Ensembl)
COLGALT1GeneProductENSG00000130309 (Ensembl)
CREB3L1GeneProductENSG00000157613 (Ensembl)
CRTAPGeneProductENSG00000170275 (Ensembl)
Ca2+MetaboliteCHEBI:29108 (ChEBI)
FKBP10GeneProductENSG00000141756 (Ensembl)
FZD1GeneProductENSG00000157240 (Ensembl)
IFITM5GeneProductENSG00000206013 (Ensembl)
ITPR1GeneProductENSG00000150995 (Ensembl)
K+MetaboliteCHEBI:29103 (ChEBI)
LOXGeneProductENSG00000113083 (Ensembl)
LRP5GeneProductENSG00000162337 (Ensembl)
LRP6GeneProductENSG00000070018 (Ensembl)
MBTPS1GeneProductENSG00000140943 (Ensembl)
MBTPS2GeneProductENSG00000012174 (Ensembl)
MIA3GeneProductENSG00000154305 (Ensembl)
P3H1GeneProductENSG00000117385 (Ensembl)
P3H2GeneProductENSG00000090530 (Ensembl)
P4HA1GeneProductENSG00000122884 (Ensembl)
P4HA2GeneProductENSG00000072682 (Ensembl)
P4HBGeneProductENSG00000185624 (Ensembl)
PLOD1GeneProductENSG00000083444 (Ensembl)
PLOD2GeneProductENSG00000152952 (Ensembl)
PPIBGeneProductENSG00000166794 (Ensembl)
SERPINF1GeneProductENSG00000132386 (Ensembl)
SERPINH1GeneProductENSG00000149257 (Ensembl)
SP7GeneProductENSG00000170374 (Ensembl)
TMEM38BGeneProductENSG00000095209 (Ensembl)
TNFRSF11AGeneProductENSG00000141655 (Ensembl)
TNFRSF11BGeneProductENSG00000164761 (Ensembl)
TNFSF11GeneProductENSG00000120659 (Ensembl)
WNT1GeneProductENSG00000125084 (Ensembl)

Annotated Interactions

No annotated interactions

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