10.12.2012 Views

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

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

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

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Document<br />

drug from the pocket is confirmed <strong>by</strong> crystallographic analysis showing that the Phe side chain in the<br />

Cys rarrow.gif Phe mutation occupies the site which would be occupied <strong>by</strong> a drug if it were bound.<br />

B. Compensation Mutants<br />

Page 515<br />

More intriguing and more difficult to understand are the compensation mutants. These viruses bind<br />

compounds within their hydrophobic pockets, but are still able to replicate and are therefore able to<br />

compensate for the bound drug (Table 1, Figure 4). These mutations, like the mutations that convey acidresistance<br />

phenotypes, cluster about the hydrophobic pocket of VP1 [27,28,92].<br />

Two hypothesis have been presented in order to explain the behavior of the compensation mutants. The<br />

first suggests that there is a link between the binding of receptor <strong>by</strong> virion and its ability to bind<br />

compounds in the VP1 pocket. The second hypothesis suggests that the effect of a mutation on protein<br />

stability leads to the drug-resistant phenotype. These two hypotheses are not mutually exclusive.<br />

Linked-Binding Hypothesis<br />

The compensation mutants can be subdivided into those that occur on the canyon floor and those that are<br />

inside the VP1 hydrophobic pocket. The linked-binding hypothesis suggests that the subset of<br />

compensation mutations that occur on the canyon floor increase the binding affinity of receptor. An<br />

increase in binding for one of these mutants, Val1153 rarrow.gif Ile, has been observed [28]. This<br />

increased binding would then in turn cause a decrease in the affinity of the capsid for the drug. This<br />

would result in the drug being less effective in inhibiting uncoating.<br />

The second subset of compensation mutants are those that occur inside the hydrophobic pocket but do<br />

not interact with the receptor binding site. These mutations might directly decrease drug-binding affinity<br />

in the VP1 pocket due to decreased hydrophobic interactions caused <strong>by</strong> the smaller amino acid side<br />

chains [27]. In both subsets of mutations, the binding affinity of a drug is reduced either directly or<br />

through the effects of receptor binding. This decreased affinity for drug would be displayed as a drugresistant<br />

phenotype.<br />

Stabilization—Destabilization Hypothesis<br />

An alternative explanation for the behavior of the drug compensation mutants suggests that these<br />

mutants allow for increased conformational flexibility in the capsid. This increased conformational<br />

flexibility would compensate for the decrease in flexibility, which is manifested <strong>by</strong> decreased acid or<br />

thermal lability, induced <strong>by</strong> the binding of drug. The increase in flexibility would allow a<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_515.html [4/9/2004 12:45:42 AM]

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!