Biology Reference
In-Depth Information
6.2 Catalytic Domain
6.2.1 Full Length of Active Site of MMP-12 May Interact
with Elastin
The catalytic domains of MMP-12 (macrophage elastase or metalloelastase) and
MMP-7 are distinctive among MMPs in their sufficiency to cleave elastin fibrils
(Busiek et al.
1992
; Shapiro et al.
1993
; Imai et al.
1995
; Gronski et al.
1997
), which
are long-lived and resistant to proteolysis and acid hydrolysis. At least three dozen
of the sites that MMP-12 hydrolyzed within insoluble elastin from human skin
were identified by mass spectrometry. The sites clustered near the termini and
most commonly at G-L peptide bonds, as well as at G-V and A-L linkages (Taddese
et al.
2008
). The docking to MMP-12 of peptide sequences encompassing several of
these cleavage sites was simulated with guidance by ambiguous NMR chemical
shift mapping of effects of dilute, solubilized elastin on NMR spectra. The
simulated structural models place the peptides linearly across the active site cleft
with four to six residues on the unprimed (“left”) side of the scissile bond and three
or four on the primed (“right”) side (Bertini et al.
2009
,
2009b
). Such models are
conventional and consistent with the previous models of peptides docked to MMPs
such as MMP-12 (Lang et al.
2001
; Bertini et al.
2006
). Several MMP-12 residues
along the length of the active site cleft often formed hydrogen bonds to peptides
from elastin in the structural simulations (Bertini et al.
2009
,
2009b
) (Fig.
6.2
).
Recent NMR and protein engineering measurements corroborate elastin interac-
tions with these residues but implicate Thr210 and Gly227 in the active site cleft as
well (Palmier et al.
2010
) (Fig.
6.3
).
Fig. 6.2 Chemical groups of the backbone of MMP-12 predicted to form hydrogen bonds with
linearized peptide fragments of elastin. This is based on structural simulations of how the peptides
may dock when guided by NMR chemical shift mapping (Bertini et al.
2009
,
2009b
). The active
site cleft is shown in the standard orientation. The color code is
gray
for the active site zinc,
brown
for the calcium ion nearest the active site,
red
for carbonyl oxygen hydrogen bond acceptor,
cyan
for carbon,
white
for amide hydrogen bond donor, and
blue
for amide nitrogen. The chemical
groups are plotted largest when engaged in a hydrogen bond with the elastin peptides in almost all
the structural models, with medium thickness H-bonded in a majority of structural models, and
smallest thickness when H-bonded in a significant minority of the cases. The NMR structure
represents the ligand-free state of human MMP-12(E219A) (Bhaskaran et al.
2007
)
