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1915

CHAPTER 113 MOLECULAR BIOLOGY AND

MOLECULAR BIOLOGY AND BIOCHEMISTRY OF THE COAGULATION
FACTORS
BIOCHEMISTRY OF THE THE VITAMIN K–DEPENDENT ZYMOGENS:

COAGULATION FACTORS AND PROTHROMBIN, FACTOR VII, FACTOR IX,
FACTOR X, AND PROTEIN C
PATHWAYS OF HEMOSTASIS The vitamin K-dependent zymogens circulate in an inactive state and
require proteolytic activation to function as a serine protease. All share
a similar domain structure of a C-terminal serine protease domain and
an N-terminal γ-carboxy glutamic acid (Gla) domain, which are con-
Mettine H. A. Bos, Cornelis van ‘t Veer, and Pieter H. Reitsma nected by two epidermal growth factor (EGF)-like domains or kringle
domains (Fig. 113–1). Each protein domain has a well-defined function
and facilitates substrate recognition, interaction with protein cofactors,
SUMMARY or binding to a negatively charged lipid surface, such as that of activated
platelets or endothelial cells, thereby restricting coagulation to the site
of injury. The latter is mediated via the Gla domain, a domain that is
The coagulation cascade consists of a complex network of reactions that are characteristic to the vitamin K–dependent proteins.
essential for the conversion of zymogens into enzymes and of inactive pro- The high level of protein and gene homology suggests that the vita-
cofactors into cofactors. Most of these reactions take place on a membrane min K–dependent zymogens originate from a common ancestral gene
surface, which restricts coagulation to the site of injury. Upon initiation, these as a result of gene duplications. Exon shuffling and tandem duplication
1
reactions serve to produce the fibrin that is necessary for the formation of a may account for the generation of the ancestral gene, in which the func-
stable hemostatic plug. In addition, these reactions provide feedback loops tional domains that are encoded by a single exon each were combined
that limit and localize thrombus formation and regulate thrombus resolution. and duplicated. This process may also account for the presence of the
2
This chapter highlights key biochemical characteristics of the individual coag- kringle domains as opposed to EGF-like domains in prothrombin.
ulation factors, essential aspects regarding their synthesis, and the clinical The Gla domain refers to the 42-residue region located in the
importance of acquired or inherited variations that affect their quantity or N-terminus of the mature protein that comprises 9 to 12 glutamic acid
function. The coagulation factors are grouped as (1) the vitamin K-dependent residues that are posttranslationally γ-carboxylated into Gla residues
zymogens (prothrombin, factor VII, factor IX, factor X, and protein C); (2) the by a specific γ-glutamyl carboxylase in the endoplasmatic reticulum of
hepatocytes. This γ-carboxylase requires oxygen, carbon dioxide, and
3
procoagulant cofactors (factor V, factor VIII); (3) the soluble cofactors (pro- the reduced form of vitamin K for its action, hence the name vitamin
tein S, von Willebrand factor); (4) factor XI and the contact system (factor XII, K–dependent proteins. For each Glu residue that is carboxylated, one
prekallikrein, and high-molecular weight kininogen); (5) the cell-associated molecule of reduced vitamin K is converted to the epoxide form
cofactors (tissue factor, thrombomodulin, endothelial protein C receptor); (Fig. 113–2). Vitamin K epoxide reductase converts the epoxide form of
(6) the fibrin network (fibrin[ogen], factor XIII, thrombin-activatable fibrinoly- vitamin K back to the reduced form. Warfarin and related 4-hydroxy-
4
sis inhibitor); and (7) inhibitors of coagulation (antithrombin, tissue factor coumarin–containing molecules inhibit the activity of vitamin K epox-
pathway inhibitor, protein Z/protein Z-dependent protease inhibitor). Table ide reductase, thereby preventing vitamin K recycling and inhibiting
113–1 summarizes the major features of the coagulation factors addressed γ-carboxylation. This results in a heterogeneous population of circulat-
in this chapter. The final sections of this chapter present an overview of the ing undercarboxylated forms of the vitamin K–dependent proteins with
coagulation cascade in which the pathways of hemostasis including the contri- reduced activity. Because warfarin blocks the reductase and not the car-
bution of endothelial cells, blood platelets, and immune cells are described. boxylase, the inhibitory effect of warfarin can be (temporarily) reversed
by administration of vitamin K. Recognition by and interaction with
γ-carboxylase is facilitated by the propeptide sequence that is located
C-terminal to the signal peptide. The propeptide is highly conserved
among the vitamin K–dependent proteins, and amino acids at positions
–18, –17, –16, –15, and –10 are critical to recognition by the γ-carboxylase.
5,6
Acronyms and Abbreviations: APC, activated protein C; ADP, adenosine diphos- Following γ-carboxylation, the propeptide is removed through limited
phate; AT, antithrombin; C4BP, complement 4b–binding protein; COX, cycloox- proteolysis prior to secretion of the mature protein.
ygenase; EGF, epidermal growth factor; EPCR, endothelial protein C receptor; A correctly γ-carboxylated Gla domain is essential for interac-
ER, endoplasmatic reticulum; ERGIC, ER-Golgi intermediate compartment; Gla, tion of the vitamin K–dependent proteins with phosphatidylserine,
γ-carboxy glutamic acid; GP, glycoprotein; HK, high-molecular-weight kininogen; a negatively charged phospholipid. Under normal conditions, phos-
LMAN1, mannose-binding lectin-1; PAI-1, plasminogen activator inhibitor type 1; phatidylserine is not exposed on the outer membrane leaflet of cells.
PAR, protease-activated receptor; PK, prekallikrein; poly-P, polyphosphate; RVV, However, in activated endothelial cells or platelets, phosphatidylserine
Russell’s viper venom; SHBG, sex hormone–binding globulin; TAFI, thrombin-activat- is part of the extracellular cell surface where it supports blood coagu-
able fibrinolysis inhibitor; TFPI, tissue factor pathway inhibitor; UFH, unfractionated lation reactions. The Gla domain interacts with the anionic cell surface
heparin; VWD, von Willebrand disease; VWF, von Willebrand factor; ZPI, protein Z– in a calcium-dependent manner. These calcium ions are coordinated
dependent protease inhibitor. by Gla residues and induce a conformational change in the Gla domain
that is characterized by the appearance of a hydrophobic surface loop

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