204
5 Plasma Proteins, Yolk Proteins and Metal-Binding Proteins
proteolysis, glycosylation and sulphation of a precursor of 2813 amino acids and is constructed
from two to five repeats of each of four different
types of domain. The vWF mosaic gene is
undoubtedly the result of evolutionary processes
such as exon shuffling and the duplication of fragments from very different genes. Parts of the
sequence are in fact homologous to the vitellogenin of the nematode Caenorhabditis e/egans
[14, 153, 255]. In the intact organism, the clotting
cascade is more often induced by the tissue factor
TF (thromboplastin), which activates plasma factor VII, than by the platelet components. TF is a
membrane-bound glycoprotein with 263 amino
acids and shows no significant homology to serine
proteases [238]. Factor VII is a serine protease
with 406 amino acids and upon activation is
cleaved into two disulphide-bridge-linked chains
of 156 and 254 amino acids [195]. Contact with
various negatively charged materials activates
only the intrinsic pathway in isolated blood. This
involves the factors XII and XI, prekallikrein and
the high molecular weight kininogen (HMWK).
Pre kallikrein is found in human blood plasma as a
complex with HMWK and is converted by factor
XIIa to active kallikrein, which itself consists of
two chains bound by a disulphide bridge. Kallikrein releases kinin from kininogen and activates
plasminogen, factor IX and the surface-bound
factor XII. A further action of kallikrein is the
production of the pharmacologically active nonapeptide bradykinin from HMWK; the remaining
product is a molecule, made up of two chains,
which further promotes clotting [277]. In addition
to HMWK, which has a molecular mass of
110 kDa, there are also smaller kininogens
(LMWK) corresponding to the N-terminus of
HMWK. Rats possess a K gene for HMWK and
LMWK and also two homologous T genes, which
differ markedly from the K gene due to the insertion of an Alu element and a frame-shift mutation
in the HMWK region. Both HMWK and LMWK
function as cysteine-proteinase inhibitors [132].
The structure and evolution of the individual
components of the human clotting cascade will be
only briefly referred to here as unfortunately
there are no comparative biochemical data. Factor XI is a homodimer that, when complexed with
HMWK and phospholipid, is cleaved by the
action of factor XIIa into two light and two heavy
chains; in the presence of Ca z + it can then activate factor IX. Factor XI agrees in 58 % of its
sequence with human prekallikrein [80, 284].
Factor IX belongs, together with factors VII and
X, prothrombin and the clotting-inhibitory proteins C and S, to the vitamin K-dependent proteins,
which are all homologous [262]. In all these proteins, the first 10-12 glutamine residues of the
chain are converted to y-carboxylglutamic acid
(Gla) residues by the action of a vitamin K
(phyllochinon)-dependent
carboxylase
(see
Fig. 3.1, p. 72). These Gla residues bind Ca z + and
thereby allow the interaction of the clotting factors with phospholipids. The primary translation
products of the relevant genes always consist of a
signal peptide, a propeptide which is perhaps
involved in Gla formation, the Gla region, two
domains homologous to the epidermal growth
factor (EGF), a connecting region, and the catalytic domain that is homologous to the usual
serine proteases; the vitamin K-dependent proteins are model examples of evolution by exon
shuffling [262] (see Fig. 3.6, p.91). Factor X, as
found in the plasma, consists of a light chain
(15 kDa) and a heavier chain (40 kDa) bound
together by a disulphide bridge. The light chain
includes 12 y-carboxylglutamic acid residues, and
the heavy chain contains the active centre. In
man, the non-enzymatic factors V and VIII are
very large proteins which were first sequenced via
the cDNA. The 2224 and 2332 amino acids,
respectively, of these two factors are subdivided
into three A regions of 330 amino acids, a B region of 980 amino acids and two C regions of
220 amino acids in the order AI-A2-B-A3-ClC2. The two factors show about 40 % sequence
similarity; their A regions share 35-40 % similarity with the copper protein caeruloplasmin [120].
It may be assumed from the results of physiological investigations that the blood-clotting process progresses similarly in all vertebrates,
although with some quantitative differences.
However, comparative biochemical data are only
available for fibrinogen. Human fibrinogen is a
glycoprotein of 340 kDa with about 4 % carbohydrate; it is symmetrically constructed from an
Aa chain of 610 amino acids, a B~ chain of 461
amino acids and a y chain of 411 amino acids,
according to the formula (Aa, B~, y)z. Thrombin
cleaves with high specificity an arginine-glycine
bond in the Aa and B~ chains, thereby setting
free the short -chained fibrinopeptides A and B
and producing the soluble fibrin monomers (a,
~, y)z. The polymerization and precipitation of
the monomers to the insoluble fibrin clots is a
very complicated process involving all three
chains [175,284], in the course of which the factor
XIII a (glutaminylpeptide-y-glutamyltransferase)
forms isopeptide bonds between glutamine-ycarbamoyl and lysine-E-amino groups (Fig. 5.2).
5 Plasma Proteins, Yolk Proteins and Metal-Binding Proteins
proteolysis, glycosylation and sulphation of a precursor of 2813 amino acids and is constructed
from two to five repeats of each of four different
types of domain. The vWF mosaic gene is
undoubtedly the result of evolutionary processes
such as exon shuffling and the duplication of fragments from very different genes. Parts of the
sequence are in fact homologous to the vitellogenin of the nematode Caenorhabditis e/egans
[14, 153, 255]. In the intact organism, the clotting
cascade is more often induced by the tissue factor
TF (thromboplastin), which activates plasma factor VII, than by the platelet components. TF is a
membrane-bound glycoprotein with 263 amino
acids and shows no significant homology to serine
proteases [238]. Factor VII is a serine protease
with 406 amino acids and upon activation is
cleaved into two disulphide-bridge-linked chains
of 156 and 254 amino acids [195]. Contact with
various negatively charged materials activates
only the intrinsic pathway in isolated blood. This
involves the factors XII and XI, prekallikrein and
the high molecular weight kininogen (HMWK).
Pre kallikrein is found in human blood plasma as a
complex with HMWK and is converted by factor
XIIa to active kallikrein, which itself consists of
two chains bound by a disulphide bridge. Kallikrein releases kinin from kininogen and activates
plasminogen, factor IX and the surface-bound
factor XII. A further action of kallikrein is the
production of the pharmacologically active nonapeptide bradykinin from HMWK; the remaining
product is a molecule, made up of two chains,
which further promotes clotting [277]. In addition
to HMWK, which has a molecular mass of
110 kDa, there are also smaller kininogens
(LMWK) corresponding to the N-terminus of
HMWK. Rats possess a K gene for HMWK and
LMWK and also two homologous T genes, which
differ markedly from the K gene due to the insertion of an Alu element and a frame-shift mutation
in the HMWK region. Both HMWK and LMWK
function as cysteine-proteinase inhibitors [132].
The structure and evolution of the individual
components of the human clotting cascade will be
only briefly referred to here as unfortunately
there are no comparative biochemical data. Factor XI is a homodimer that, when complexed with
HMWK and phospholipid, is cleaved by the
action of factor XIIa into two light and two heavy
chains; in the presence of Ca z + it can then activate factor IX. Factor XI agrees in 58 % of its
sequence with human prekallikrein [80, 284].
Factor IX belongs, together with factors VII and
X, prothrombin and the clotting-inhibitory proteins C and S, to the vitamin K-dependent proteins,
which are all homologous [262]. In all these proteins, the first 10-12 glutamine residues of the
chain are converted to y-carboxylglutamic acid
(Gla) residues by the action of a vitamin K
(phyllochinon)-dependent
carboxylase
(see
Fig. 3.1, p. 72). These Gla residues bind Ca z + and
thereby allow the interaction of the clotting factors with phospholipids. The primary translation
products of the relevant genes always consist of a
signal peptide, a propeptide which is perhaps
involved in Gla formation, the Gla region, two
domains homologous to the epidermal growth
factor (EGF), a connecting region, and the catalytic domain that is homologous to the usual
serine proteases; the vitamin K-dependent proteins are model examples of evolution by exon
shuffling [262] (see Fig. 3.6, p.91). Factor X, as
found in the plasma, consists of a light chain
(15 kDa) and a heavier chain (40 kDa) bound
together by a disulphide bridge. The light chain
includes 12 y-carboxylglutamic acid residues, and
the heavy chain contains the active centre. In
man, the non-enzymatic factors V and VIII are
very large proteins which were first sequenced via
the cDNA. The 2224 and 2332 amino acids,
respectively, of these two factors are subdivided
into three A regions of 330 amino acids, a B region of 980 amino acids and two C regions of
220 amino acids in the order AI-A2-B-A3-ClC2. The two factors show about 40 % sequence
similarity; their A regions share 35-40 % similarity with the copper protein caeruloplasmin [120].
It may be assumed from the results of physiological investigations that the blood-clotting process progresses similarly in all vertebrates,
although with some quantitative differences.
However, comparative biochemical data are only
available for fibrinogen. Human fibrinogen is a
glycoprotein of 340 kDa with about 4 % carbohydrate; it is symmetrically constructed from an
Aa chain of 610 amino acids, a B~ chain of 461
amino acids and a y chain of 411 amino acids,
according to the formula (Aa, B~, y)z. Thrombin
cleaves with high specificity an arginine-glycine
bond in the Aa and B~ chains, thereby setting
free the short -chained fibrinopeptides A and B
and producing the soluble fibrin monomers (a,
~, y)z. The polymerization and precipitation of
the monomers to the insoluble fibrin clots is a
very complicated process involving all three
chains [175,284], in the course of which the factor
XIII a (glutaminylpeptide-y-glutamyltransferase)
forms isopeptide bonds between glutamine-ycarbamoyl and lysine-E-amino groups (Fig. 5.2).