Biomedical Engineering Reference
In-Depth Information
9.2 Peptide Modulators
9.2.1 Synthetic LEKTI Domains
Mapping of the LEKTI inhibitory domains in terms of KLK inhibition was
performed in detail.
74-76
KLK5, 7, and 14 were inhibited by LEKTI D8-11 and
LEKTI D5,
75
while KLK5 and KLK7 were also inhibited by LEKTI D6.
74,76
Importantly, complexes of LEKTI with KLKs are reversible, dependent on pH.
Lower pH values result in dissociation of complex formation and release of active
protease, as shown in the epidermis where a pH gradient between the inner and
outer layers regulates the activity of the KLK cascade that controls skin des-
quamation.
11,75,77,78
Given the established importance of KLK5 and KLK7 in
skin diseases, LEKTI D6 (domain 6) (compound 9.1) was designed and syn-
thesized according to the fragment condensation method and regioselective dis-
ulfide bond formation.
79
9.1 inhibited KLK5 with an IC
50
of 125 nM; a
recombinant form of LEKTI D6 produced in E. coli showed equivalent activity
(IC
50
ΒΌ
134 nM).
H-E1-S-G-K-A-T-S-Y-A-E-L-C-N-E-Y-R-K-L-V-R-N-G-K-L-A-C-T-R-E-N-D-P-I-Q-G-P-
D-G-K-V-H-G-N-T-C-S-M-C-E-V-F-F-Q-A-E-E-E-E-K-K-K-K-E-G-E-S-R-N
68
-OH
9.1
9.2.2 Cyclic Peptide Inhibitors
Generally, a cyclized peptide is less flexible and usually shows a higher anity
for its molecular target. In addition, cyclization increases peptide bioavailability,
as it renders the peptide resistant to proteolytic degradation by exoproteases.
Peptide inhibitors for KLK2 were designed based on linear inhibitory peptides
isolated by phage display.
80
The cyclized peptides (head-to-tail cyclization) were
stable in plasma when compared to linear peptides and required more that 4 h
for complete trypsin digestion (57% for 4 h) compared to 30 min for linear
peptides.
81
Attempts to produce cyclic peptide inhibitors against KLK1 based
on the bradykinin sequence had limited success, and their K
i
was about 10 mM.
82
9.2.3 Peptide Activators of KLKs
It was found that an inactive form of mature KLK3/PSA is present in the
serum of prostate cancer patients.
83
Using X-ray crystallography, it was shown
that the kallikrein loop can adapt two different conformations: the 'open form,'
which is enzymatically active, and the 'closed form,' which is inactive.
55
Anti-
bodies that bind and stabilize the open conformation increase the activity of
KLK3/PSA.
55
Such a specific monoclonal antibody was developed and named
8G8F5,
83
and its three-dimensional structure complexed with KLK3/PSA was
resolved.
55
The rational development of KLK3/PSA activators is based on the
