netLibrary - eBook Summary Structure-based Drug Design by ...

Document
Page 452
ligand and the machinery of signal transduction, namely JAK2. It was found that both intact murine IFNγ
and its C-terminal peptide (95–133) are capable of specifically mediating an increase in the degree of
association between the recombinant, soluble IFN-γ receptor and JAK2. These findings were further
supported as IFN-γ and IFN-γ (95–133) caused an increase in the amount of JAK2 coprecipitating with
the receptor from intact murine macrophages [58]. This has been the first such demonstration of an
extracellular cytokine ligand participating directly in interaction with cytoplasmic signaling elements.
E. IFN-γ as a Candidate for Rational Drug Design
The IFN-γ molecule is a potentially attractive model for the rational application of drug-design
strategies. Reagents exist that are capable of either positively or negatively modulating the in vivo
effects of IFN-γ. An initial target is quite simply at the level of receptor-ligand interaction. Synthetic
peptide analogs of the N-terminal region have been successfully applied in vitro to inhibit interaction of
intact IFN-γ with cell-surface receptors [30]. Interestingly, it has been observed that the N-terminal
region of mouse IFN-γ has the ability to interact with the human receptor [59]. It was shown that the
mouse peptide IFN-γ (1–39) had a 10-fold greater ability to block the binding of human IFN-γ to cellsurface
receptors. This was shown to be correlated with a more stable structure in solution for the
murine peptide and illustrates the importance of stable structure to receptor binding, which may be
exploited when designing peptide mimetics. The solution structure of this peptide has also been
determined and could provide the beginning steps for determining the structural requirements of an
antagonist [7]. Future studies could focus on cocrystallization of the peptides with receptor or NMR
studies of peptide domains of the receptor and IFN-γ. Recombinant, soluble forms of the extracellular
domain of the ligand-binding subunit of the receptor have also been used in analogous fashion both in
vitro to inhibit cell-surface binding and in vivo to interfere with disease progression [60]. Therefore
prevention of potentially deleterious effects of IFN-γ may be achieved by preventing initial interactions
with receptor molecules at the cell surface.
A second candidate region lies within amino acid residues 84–94 of human IFN-γ and the corresponding
region of its murine homologue. This portion of the molecule functions as a nuclear localization signal
and, therefore, is also an attractive target for drug design. In cells treated with IFN-γ, the IFN-γ molecule
traffics rapidly to the nucleus of the cell, usually within one to two minutes. When the IFN-γ molecule is
crosslinked to its receptor, the resultant receptor-ligand complex migrates to the nucleus [40]. The
implication is that this sequence may therefore be of use in artificially targeting proteins from the
cytoplasm directly to the nucleus. This is potentially a very attractive method
http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_452.html [4/9/2004 12:12:03 AM]