Introduction:
Structure
aided design of HIV PR inhibitors has led to a class of drugs useful in
clinical anti-HIV intervention. Nevertheless, mutational development of
HIV PR drug resistance presents a major medical complication. Thus, the
present state of anti-AIDS therapies calls for design of novel compounds
that would overcome the problem of HIV PR resistance to the current
drugs.
Recently,
a combinatorial chemistry approach yielded a series of novel pluripotent
HIV PR inhibitors having a picomolar range of their Ki values for
the wild-type HIV PR as well as various degree of insensitivity of their
inhibitory potency to HIV PR mutations conferring Saquinavir, Ritonavir
and Indinavir resistances [1]. Detailed kinetic analysis of three chosen
inhibitors has, in certain cases, shown even somewhat better inhibition
of a drug-resistant HIV PR mutant in comparison to the wild-type enzyme
[1].
Crystallographic
studies of complexes:
Three most potent inhibitors and
several HIV-1 PR resistant mutants (see Table 1)
|
Table 1 |
Inhibitor |
HIV PR mutants |
| |
Z-Apb-Glu-Hph-NH2 |
G48V/L90M
HIV-1 PR, resistance to Saquinavir |
| |
Z-Pns-Phe-Glu-Glu-NH2 |
M46I/V82T/I84V/A71V
HIV-1 PR, resistance to Indinavir |
| |
Z-Pst-Glu-Hph-NH2 |
V82A
HIV-1 PR, resistance to Ritonavir |
I
Results
(current status):
Most of the complexes from the series
were succesfully crystallized, several structures were solved and
refined.
Depending on the excess of inhibitor used for the complex formation, the
HIV-1 protease complexed with a Z-Apb-Glu-Hph-NH2
(phenylnorstatine inhibitor forms
crystals of either hexagonal hexagonal (P61) or orthorhombic (P212121)
symmetry. The
orthorhombic form shows unusual complexity of crystal packing: in
addition to one inhibitor molecule bound to the enzyme active site, the
second inhibitor molecule is bound as an outer ligand at the protein
interface Figure 1). Binding of the outer ligand apparently increases
parameters of crystal quality so that the diffraction data permitallow
to solve the structure of the complex at 1.03 Å
[2], the best resolution reported up to
date. Parameters of solved structures of the orthorhombic and hexagonal
form (PDB codes: 1hn0,
1u8g)
were compared [3].
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Figure 1:
T
Crystal Packing.
One
unit cell is shown.
Protein
molecules are represented by ribbon models, colored red for
the molecule in the asymmetric part of the unit cell, and
colored green, blue, and yellow for the first, second and
third symmetry related molecules, respectively. Stick models,
colored orange for the molecules bound in the active site,
and magenta for the molecules contacting the outer protein
surface, represent the inhibitor molecules.
|
References:
[1]
[2]
Brynda J., Rezacova P., Fabry M., Horejsi M., Stouracova R., Sedlacek J.,
Soucek M., Hradilek M., Lepsik M., Konvalinka J. (2004): A Phenylnorstatine
Inhibitor Binding to HIV-1 Protease: Geometry, Protonation, and Subsite-Pocket
Interactions Analyzed at Atomic Resolution. J. Med. Chem 47:
2030-2036 [MEDLINE]
[3]
Brynda J., Rezacova P., Fabry M., Horejsi M., Stouracova R., Soucek M.,
Hradilek M., Konvalinka J., Sedlacek J.: Inhibitor binding at
the protein interface in crystals of a HIV-1 protease complex. Acta
Cryst. (2004) D60:1943-1948 [MEDLINE]
