General overview of blood clot formation and elimination. Flashcards
(35 cards)
1
Q
Fibrinogen (Factor I)
A
- water soluble plasma glycoprotein
- converted to fibrin by thrombin
- synthesized in liver by hepatocytes
- concentration of fibrin: 200-400 mg/dl
- hexamer (2a, 2B, 2y)
- 2 D + 1E domain
- E domain: N-terminal of all peptides + disulfide bonds
- D domain: b and y polypeptide C-terminals
- alpha chain folds back ⇒ alphaC domain
2
Q
Fibrin
A
- Thrombin proteolyse fibrinogen, cleaves alpha-chain N terminal ⇒ release fibrinopeptide A ⇒ thrombin cleaves beta chains fibrinopeptide B ⇒ fibrin monomers ⇒ polymerize spontaneously to insoluble gel
- held together by noncovalent and electrostatic forces
- stabilized by factor XIIIa
3
Q
Factor XIII
A
- fibrin stabilizing factor
- transglutaminase enzyme
- crosslinks fibrin
- converted to active XIIIa by thrombin
- glycoprotein heterotetramer (2a, 2B)
- also present as homodimer (2a) in platelets
- alpha-subunit develops in megakaryocytes and monocytes, beta-subunit develops in liver
- A subunit: transglutaminase part, adds alkyl group to nitrogen on glutamine residue ⇒ bind with lysine ⇒ expel ammonia and create isopeptide bond between LYs and Gln
- B subunit: no enzymatic activity, carrier for A subunit or regulator subunit
4
Q
Activation of prothrombin
A
Factor Xa catalyses cleavage of prothrombin at two sites between Arg271-Thr272 and Arg320-Ile321 ⇒ thrombin and single polypeptide strand(binds Ca2+)
- maximal ROR when complex bound to phospholipid membrane at phosphatidylserine residues
- Ca2+ must be present
5
Q
Prothrombinase complex
A
- consists of: serine protease, Factor Xa, Factor Va
- assembles on negatively charged phospholipid membranes in presence of Ca2+
- catalyses: prothrombin (factor II) ⇒ mezothrombin ⇒ thrombin (factor IIa)
- held together by non-covalent interactions
6
Q
Factor Va
A
- composed of heavy and light chain
- bind to negatively charged phospholipid membranes
- receptor for membrane bound Factor Xa
- increases the rate of reaction of prothrombinase complex
7
Q
Vitamin K
A
- involved in carboxylation of Glu residues⇒ gamma-carboglutamate residues⇒ involved in binding calcium
- vital for prothrombin, factors VII, IX and X and proteins C,S and Z
8
Q
Warfarin
A
- medication for regular blood clots
- inhibit Vitamin K epoxide reductase (⇒ no vit K reduced ⇒ no Gla)
9
Q
Common risk factors for clotting
A
Trauma
Family history
Long haul flight
Cancer
10
Q
Tissue factor pathway (extrinsic)
A
- Damage to blood vessel
- Factor VII comes in contact with TF ⇒ TF-FVIIa
- TF-FVIIa activates Factor IX and X
- Factor VII is activated by FXIa, FXII, FXa
- Factor X activation immediately inhibited by TFPI
- FXa + FVa form prothrombinase complex ⇒ prothrombin to thrombin
- Thrombin activates FV, FVIII and activates + released FVIII from vWF
- FVIIIa + FIXa form tenase complex ⇒ activate FX
11
Q
Contact activation pathway (intrinsic)
A
- Formation of primary complex by HMWK, prekallikrein and Factor XII
- Prekallikrein ⇒ kallikrein, Factor XII ⇒ Factor XIIa
- Factor XIIa converts Factor XI⇒Factor XIa
- Factor XIa activates Factor IX ⇒ forms tenase complex with Factor VIIIa
- Tenase complex activates FX⇒FXa
- during inflammation, bacteria and neutrophil needed for XII auto activation
- depending on substrate of kallikrein ⇒ release bradykinin ⇒ release of plasminogen activator ⇒ activate prourokinase
12
Q
Functions of Thrombin
A
- converts FXI⇒XIa, VIII⇒VIIIa, V⇒Va, fibrinogen⇒ fibrin, XIII⇒XIIIa
- thrombin + thrombomodulin activates protein C + inhibits fibrinolysis by cleaving TAFI
- promotes platelet activation and aggregration
13
Q
Thrombin inhibitors
A
- Antithrombin/ heparin
- Heparin co-factor II/ heparin sulphate
- alpha-1 protease inhibitor
- alpha-2 macroglobulin
14
Q
Factor Xa inhibitors
A
- TFPI
2. Protein Z cofactor and inhibitor
15
Q
Antithrombin
A
- glycoprotein
- produced in liver
- contains 3 disulfide-bonds, 4 glycosylation sites
- alpha-antithrombin is dominating- has all 4 sites occupied by oligosaccharides
- beta- antithrombin- 1 site not occupied, activity increases with heparin, enhances binding to FII, FX
- inhibits: thrombin, VIIa, IXa, Xa, XIa
16
Q
Heparin
A
- highly sulfated glycosaminoglycan
- synthesized in mast cells
- anticoagulant
- heparin + AT3 + thrombin
- heprain + AT3 + Xa
- increases the ROR of thrombin-antithrombin
- indirect inhibitor of thrombin
17
Q
Hirudin
A
- natural peptide in salivary glands of leeches
- most potent inhibitor of thrombin
- high affinity to thrombin bc can bind to active site + anion binding site of fibrinogen
- binds to and inhibits the activity of thrombin
18
Q
Plasma-FXIII
A
- inactive because b-subunits block alpha-subunit active site
- thrombin needed for activation
- Ca2+ helps with beta-subunit dissociation
- co-factor: Fibrin
19
Q
Platelet-FXIII
A
- no activation required
- platelet must first be activated ⇒ Ca2+ conc. reaches threshold for FXIII activation
20
Q
FXIII deficiency
A
- autosomal, recessive
- umbilical cord bleeding, sbcutaneous bleeding, sub muscular bleeding, intracranial bleeding
- recombinant A subunit can be given as treatment
21
Q
Characteristics of thrombin
A
- serine protease family
- hydrolyses peptide bonds- max 2/protein
- high specificity
- consists of 2 polypeptide chains, with disulfide bonds
22
Q
Factors with Gla domain
A
F II F VII F IX F X Protein S Protein Z APC
23
Q
Positive feedback of Thrombin
A
F VIII
F XI
F V
24
Q
Tissue Factor TF
A
- transmembrane protein
- present on membrane surface not in contact with blood
- results in extrinsic pathway when contact with blood
25
Protein C
- serine protease
- APC can cleave FV
- co-factor: protein S
- contains Gla domain ⇒ bind to phospholipid membrane
- antithrombotic effects: inactivates FVIII + decreases half-life of prothrombinase
- thrombin + thrombomodulin needed for activation
26
APC resistance
- mutation in FV and FVIII
- Arg506⇒ Gln
- APC cannot cleave this
⇒ half-life of prothrombinase increases
27
Significance of gamma-carboxylation
- maintain 3D structure
- form hydrophobic part ⇒ inserted to membrane + localize protein
- direct electrostatic interaction with membrane phosphatidylserine + Ca2+
28
Tissue factor inhibitor TFPI
- endogenous inhibitor, can inhibit membrane bound proteases
- can inhibit both TF-FVIIa + prothrombinase complex
- produced by endothelial cells and megakaryocytes
- 2 isoforms, TFPIalpha + TFPIbeta
- has Kunitz domain (disulfide rich alpha+beta fold)
29
TFPIa
- from endothelial cell ⇒ blood ⇒ bind to heparin sulfate
- from megakaryocyte⇒ in platelets
- K3 domain bound to Protein S (anchor FI-FVII with Gla to TFPI)
- K2 domain bound to FX
- K1 domain bound to FVIIa⇒ inhibited
30
TFPIb
- connects to endothelial membrane with GPI-anchor
- K1 domain inhibits FVIIa
- role: maintain the endothelial surface's coagulation property
- cannot inhibit prothrombinase complex ⇒ does not have 3x C-terminal
31
Heparan sulphate
- glycosaminoglycan, covalently attached to protein
- component of extracellular matrix
- produced by all cell types
32
Polyphosphate
- source: bacteria, platelet dense granule,
- short polyP:
* from platelet
* activate FV
* inhibit TFPI
* activate XI
- long polyP:
* from bacteria
* activate FXII
33
Multicomponent complexes
1. Extrinsic factor tenase:
* enzyme: VIIIa
* cofactor: TF
* substrate: X
2. Intrinsic factor tenase:
* enzyme: IXa
* cofactor: VIIIa
* substrate: X
3. Prothrombinase:
* enzyme: Xa
* cofactor: Va
* substrate: prothrombin
4. Protein C complex:
* enzyme: thrombin
* cofactor: TM (protein S)
* substrate: protein C
34
Prothrombin time PT
- time for fibrin clot to form
| - Measures function of Tissue factor pathway, thrombin, fibrinogen, FV, FXIII
35
Activated Partial Thromboplastin time aPTT
- time for fibrin clot to form
| - measures function of intrinsic pathway + common pathway
