Biology Reference
In-Depth Information
5.6 MMP-2
MMP-2 contains three repeats of a fibronectin type II (FNII) domain. This domain
binds to collagen I with an apparent
K
d
in a low micromolecule range, but less
tightly compared to gelatin (Steffensen et al.
1995
). The main MMP-2-binding site
in native collagen I is the telopeptide region and pepsin-treated collagen, which
lacks the telopeptides, does not bind to the FNII domain at 20
C (Steffensen et al.
1995
). Therefore for MMP-2 to cleave collagen I particularly at around 25
C, the
FNII domain is unlikely to interact with the collagenase-cleavage site of type I
collagen, but it may interact with the triple helical region of collagen I after denatur-
ation. In fact, MMP-2 lacking the FNII domains retains collagenolytic activity at
25
C, although it is about 50% of that of full-length MMP-2 (Patterson et al.
2001
).
Putting back the FNII domain enhances this activity about twofold. This slight
enhancement of collagenolytic activity may be due to increased collagen unwinding.
The FNII domain is located between Gly
191
and Tyr
366
in the loop between the fifth
b
-helix of the catalytic site of MMP-2. Tyr
366
corresponds
to Tyr
191
of MMP-1, one of the key residues involved in triple helicase activity.
Mutation of Tyr
191
to Thr reduces collagenolytic activity by 80% and collagen
unwinding activity by more than 90% (see Fig.
5.3
). Therefore, it would be interesting
to compare the collagen unwinding activity of MMP-2 and that of MMP-2 (
-strand and the third
a
FNII).
Gioia et al. (
2007
) measured native bovine collagen I cleavage byMMP-2 at 37
C,
and reported that MMP-2 degraded
D
2
(I) chain, suggesting that the two chains are independently cleaved. On the other hand,
they found that collagenase (MMP-8) and the ectodomain of MMP-14 cleaved three
a
chains almost simultaneously, producing
¾
a
1(I) and
a
2(I) fragments in the ratio of
2:1. At 37
C the CD spectrum of collagen I showed relaxed triple helicity and the
addition of two molar excess MMP-2 which was fully inactivated by a low molecular
weight synthetic inhibitor further relaxed to an almost completely unwound state.
These changes were interpreted to be mediated by the FNII domain. However, since
the FNII binds to the helical region of collagen only when collagen is denatured
(Steffensen et al.
1995
), the effect of FNII on collagenolysis largely depends on the
state of triple helicity of the collagen. The study of Leikina et al. (
2002
)demonstrated
that human lung collagen I gradually unfolds at 37
C (completely after a couple of
days) and even below 36
C, and the equilibrium of collagen denaturation could not be
extrapolated and complete unfolding was observed even below 36
C. However,
refolding of full-length collagen could occur below 30
C. Therefore, the degree of
unfolding of the triple helical structure must be greater at 37
Cthanat25
C.
a
1(I) chain about five times more readily than
a
5.7 MMP-14 (MT1-MMP)
MMP-14 was first discovered as a pro-MMP-2 activator (Sato et al.
1994
) and its
activity against interstitial collagens was reported by Ohuchi et al. (
1997
). Unlike
soluble collagenases such as MMP-1, -8 and -13, MMP-14 needs to dimerize on the
