Biology Reference
In-Depth Information
E259
N236
N93
S4'
R126
H
N60H
N35
G
P60B
E39
N60G
S3'
Y60A
P60C
A
E97A
W60D
C
K60F
F41
I174
R97
S2'
E36
N99
C58
C42
S2
W125
E84
M34
S1
S214
D189
G216
I65
L40
D82
E129
S3
R188
K149E
K173
R67
Y76
R187
R77A
S6
L73
R
R74
R75
F
Figure 10.3.
Schematic view of the active site canyon (bold contour) of the vitamin-K-
dependent factor ancestral protein (Krawczak
et al
., 1996). The active site triad (His57,
Asp102, Ser195, chymotrypsin numbering) is denoted by a triangle.
H: heparin-binding site, G: glycosylation site, C: chemotactic region, R: RGD sequence,
A: aryl-binding site, F: fibrinogen-binding exosite, S: specificity sites, N-terminal to
cleavage, S
: specificity sites C-terminal to cleavage. Residues that are conserved between
the vitamin-K-dependent factor ancestral protein and extant human thrombin are
circled. Those residues that have not been conserved are circled with a broken line.
(Doolittle, 1993). By contrast, both thrombin residues implicated in binding
thrombomodulin (Gln38, Arg75; Tsiang
et al
., 1995), the endothelial cell surface
thrombin receptor, were present in the ancestral protein. Thus an ancient throm-
bomodulin-like molecule might have been able to interact with the vitamin K-
dependent factor ancestral protein.
When the residues responsible for binding thrombomodulin and protein C
were excluded from the fibrinogen binding patch, five of the remaining seven
residues were found to be conserved between the vitamin K-dependent factor
ancestral protein and extant human thrombin (Lys60F, Asn60G, Asp186A,
Lys186D, Glu192) (
Figure 10.3
). Both of the altered residues (Thr60I, Asp222)
exhibit conservative changes (to Ser and Glu, respectively). These seven residues
may have constituted the original fibrinogen binding patch that was to increase in
size and binding affinity as well as diversifying functionally over evolutionary
time.
