Biology Reference
In-Depth Information
hand, pro-MMP-13 binds to collagen I with a slightly lower affinity than MMP-13
(Kn
auper et al.
1997a
), suggesting that the Hpx of pro-MMP-13 may bind to
collagen.
€
5.3
Involvement of the Catalytic, Linker and Hpx
Domains in Collagenolysis
Clark and Cawston reported that MMP-1 autocleaved the linker region when
concentrated and the Cat domain without the Hpx was no longer able to cleave
collagen I, although its activity for non-collagenolytic proteins such as casein or
synthetic peptides was retained (Clark and Cawston
1989
). Requirement of the Hpx
domain in collagenolytic activity was shown for MMP-2 (Patterson et al.
2001
),
MMP-8 (Kn
auper et al.
1993a
), MMP-13 (Kn
auper et al.
1996a
) and MMP-14 (Itoh
€
€
et al.
2006
).
To gain further insights into the structural requirements for collagenolysis, a
series of chimeras of MMP-1 or MMP-8 with MMP-3 was generated as MMP-3 has
a similar domain structural arrangement as collagenases and human MMP-1 and
human MMP-3 shares 54% identity in amino acid sequence, but does not cleave type
I and II collagens. Hybrid enzymes consisting of the Cat of MMP-1 and the linker
and Hpx of MMP-3 and the Cat of MMP-3 and the linker and Hpx of MMP-1 did not
exhibit collagenolytic activity (Murphy et al.
1992
). These results indicate that the
Hpx domain is not the sole component that is responsible for the expression of
collagenolytic activity. A similar type of chimeric study with MMP-8 and MMP-3
by Hirose et al. (
1993
) suggested that the Cat and the length of proline-rich linker of
MMP-8 are important for the expression of collagenolytic activity. Substitution of
the linker region of MMP-8 with that of MMP-3 inactivated the collagenolytic
activity. Kn
auper et al. (
1997b
) subsequently reported that the replacement of
three prolines of the MMP-8 linker with alanine reduced the collagenase activity
down to 1.5%. A single mutation of Gly
251
of the linker of MMP-1 to Asp reduced its
collagenolytic activity to 13% (Tsukada and Pourmotabbed
2002
). These results
suggest that the linker region is flexible, and it must correctly coordinate the
movement of the Cat domain and the Hpx domain.
In a study with MMP-3/MMP-1 chimeras, Chung et al. (
2000
) mapped the
RWTNNFREY (183-191) loop located between the fifth
€
b
-strand and the second
a
-helix in the Cat domain of MMP-1 as another important component in expressing
triple helicase activity. While the polypeptide folds of all catalytic domains of
MMPs are essentially identical (Bode and Maskos
2003
), the regions corresponding
to RWTNNFREY (183-191) are highly variable both in sequence and structure
among MMPs. The FNII repeats in MMP-2 and MMP-9, which influence their
substrate specificity for gelatin, type IV collagen and elastin (Murphy et al.
1994
;
Collier et al.
1992
; Shipley et al.
1996
), are also attached to this loop. This region is
located close to the S
3
0
subsite of the substrate binding groove, and Tyr
191
in the
