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- Erratum: Design of mutation-resistant HIV protease inhibitors with the substrate envelope hypothesis (Chemical Biology and Drug Design (2007) 69, (298-313)Publication . Chellappan, Sripriya; Kairys, Visvaldas; Fernandes, Miguel X.; Schiffer, Celia; Gilson, Michael K.There is a clinical need for HIV protease inhibitors that can evade resistance mutations. One possible approach to designing such inhibitors relies upon the crystallographic observation that the sub strates of HIV protease occupy a rather constant region within the binding site. In particular, it has been hypothesized that inhibitors which lie within this region will tend to resist clinically relevant mutations. The present study offers the first pros pective evaluation of this hypothesis, via compu tational design of inhibitors predicted to conform to the substrate envelope, followed by synthesis and evaluation against wild-type and mutant pro teases, as well as structural studies of complexes of the designed inhibitors with HIV protease. The results support the utility of the substrate envel ope hypothesis as a guide to the design of robust protease inhibitors.
- HIV-1 protease inhibitors from inverse design in the substrate envelope exhibit subnanomolar binding to drug-resistant variantsPublication . Altman, Michael D.; Ali, Akbar; Kumar Reddy, G. S. Kiran; Nalam, Madhavi N. L.; Anjum, Saima Ghafoor; Cao, Hong; Chellappan, Sripriya; Kairys, Visvaldas; Fernandes, Miguel X.; Gilson, Michael K.; Schiffer, Celia A.; Rana, Tariq M.; Tidor, BruceThe acquisition of drug-resistant mutations by infectious pathogens remains a pressing health concern, and the development of strategies to combat this threat is a priority. Here we have applied a general strategy, inverse design using the substrate envelope, to develop inhibitors of HIV-1 protease. Structure-based computation was used to design inhibitors predicted to stay within a consensus substrate volume in the binding site. Two rounds of design, synthesis, experimental testing, and structural analysis were carried out, resulting in a total of 51 compounds. Improvements in design methodology led to a roughly 1000-fold affinity enhancement to a wild-type protease for the best binders, from a Ki of 30–50 nM in round one to below 100 pM in round two. Crystal structures of a subset of complexes revealed a binding mode similar to each design that respected the substrate envelope in nearly all cases. All four best binders from round one exhibited broad specificity against a clinically relevant panel of drug-resistant HIV-1 protease variants, losing no more than 6–13-fold affinity relative to wild type. Testing a subset of second-round compounds against the panel of resistant variants revealed three classes of inhibitors: robust binders (maximum affinity loss of 14–16-fold), moderate binders (35–80-fold), and susceptible binders (greater than 100-fold). Although for especially high-affinity inhibitors additional factors may also be important, overall, these results suggest that designing inhibitors using the substrate envelope may be a useful strategy in the development of therapeutics with low susceptibility to resistance.
- Toward the design of mutation‐resistant enzyme inhibitors: further evaluation of the substrate envelope hypothesisPublication . Kairys, Visvaldas; Gilson, Michael K.; Lather, Viney; Schiffer, Celia A.; Fernandes, Miguel X.Previous studies have shown the usefulness of the substrate envelope concept in the analysis and prediction of drug resistance profiles for human immunodeficiency virus protease mutants. This study tests its applicability to several other thera peutic targets: Abl kinase, chitinase, thymidylate synthase, dihydrofolate reductase, and neuramini dase. For the targets where many (‡6) mutation data are available to compute the average mutation sen sitivity of inhibitors, the total volume of an inhibitor molecule that projects outside the substrate enve lope Vout, is found to correlate with average muta tion sensitivity. Analysis of a locally computed volume suggests that the same correlation would hold for the other targets, if more extensive muta tion data sets were available. It is concluded that the substrate envelope concept offers a promising and easily implemented computational tool for the design of drugs that will tend to resist muta tions. Software implementing these calculations is provided with the ’Supporting Information’.
- Design of mutation-resistant HIV protease inhibitors with the substrate envelope hypothesisPublication . Chellappan, Sripriya; Kiran Kumar Reddy, G. S.; Ali, Akbar; Nalam, Madhavi N. L.; Anjum, Saima Ghafoor; Cao, Hong; Kairys, Visvaldas; Fernandes, Miguel X.; Altman, Michael D.; Tidor, Bruce; Rana, Tariq M.; Schiffer, Celia A.; Gilson, Michael K.There is a clinical need for HIV protease inhibitors that can evade resistance mutations. One possible approach to designing such inhibitors relies upon the crystallographic observation that the sub strates of HIV protease occupy a rather constant region within the binding site. In particular, it has been hypothesized that inhibitors which lie within this region will tend to resist clinically relevant mutations. The present study offers the first pros pective evaluation of this hypothesis, via compu tational design of inhibitors predicted to conform to the substrate envelope, followed by synthesis and evaluation against wild-type and mutant pro teases, as well as structural studies of complexes of the designed inhibitors with HIV protease. The results support the utility of the substrate envel ope hypothesis as a guide to the design of robust protease inhibitors.
- Interaction of antimicrobial peptides, BP100 and pepR, with model membrane systems as explored by brownian dynamics simulations on a coarse-grained modelPublication . Alves, Carla S.; Kairys, Visvaldas; Castanho, Miguel A. R. B.; Fernandes, Miguel X.This work focuses on the conformational and dynamic properties of the antimicrobial peptides (AMPs), BP100 and pepR, when confined within model membrane systems. Brownian dynamics (BD) simulations of a coarse-grained model of each respective peptide in an environment reproducing the phospholipid bilayer were carried out. Simple mean-field potentials were used to reproduce three physically different model phosphatidylcholine (PC) membrane systems. Based on the simplicity of the peptide-membrane models used, 1 ls simulations were performed. With the appropriate choice of parameters, the structure and dynamics of each peptide were recovered from each of the simulated BD trajectories. BP100 was observed to adopt a a-helical conformation when confined in each PC membrane. For pepR under the same conditions, the formation of an N-terminal a-helix was detected, whereas the C-terminus appeared to be less ordered. The dynamic properties of each peptide were characterized in terms of local and global motions. BP100 tended to localize with no preferred orientation approximately halfway across each membrane leaflet, whereas pepR localized near the membrane core with no preferred orientation. Overall, the peptide dynamics were found to vary according to the size of the peptide, as well as the width of the membrane environment.
- SitCon: binding site residue conservation visualization and protein sequence-to-function toolPublication . Kairys, Visvaldas; Fernandes, Miguel X.We introduce SitCon (SITe CONservation), a program designed to explore conservation of functionally important sites in a series of hypothetically homologous candidate protein structures, given amino acid sequence as an input. This can especially be useful when looking for an unknown function of a protein. SitCon exploits the fact that binding sites of proteins are preserved better than the overall residue sequence conservation. To test the capability of unknown function prediction, we randomly chose known function proteins from Caenorhabditis elegans genome. To imitate a behavior of an unknown function target, only the low homology proteins with 0.01 E-score 100 were analyzed as templates. Out of 29 enzyme targets, SitCon was able to provide various hints about their function in at least 69% of the cases. For the eight nonenzyme targets, the predictions matched in only 25% of the cases. SitCon was also tested for a capability to predict presence or absence of metal-containing heterogroups in the target enzymes with 80% success rate. Because this algorithm is not based on specific protein signatures, it may allow detection of overlooked relationships between proteins. SitCon is also very effective as a tool allowing visual comparison of binding site residue conservation between the target and homologous templates side-by-side.
- Quantitative structure-activity relationship models with receptor-dependent descriptors for predicting peroxisome proliferator-activated receptor activities of thiazolidinedione and oxazolidinedione derivativesPublication . Lather, Viney; Kairys, Visvaldas; Fernandes, Miguel X.A quantitative structure–activity relationship study has been carried out, in which the relationship between the peroxisome proliferator-activated receptor a and the peroxisome proliferator activated receptor c agonistic activities of thiazo lidinedione and oxazolidinedione derivatives and quantitative descriptors, Vsite calculated in a receptor-dependent manner is modeled. These descriptors quantify the volume occupied by the optimized ligands in regions that are either com mon or specific to the superimposed binding sites of the targets under consideration. The quantita tive structure–activity relationship models were built by forward stepwise linear regression model ing for a training set of 27 compounds and vali dated for a test set of seven compounds, resulting in a squared correlation coefficient value of 0.90 for peroxisome proliferator-activated receptor a and of 0.89 for peroxisome proliferator-activated receptor c. The leave-one-out cross-validation and test set predictability squared correlation coeffi cient values for these models were 0.85 and 0.62 for peroxisome proliferator-activated receptor a and 0.89 and 0.50 for peroxisome proliferator-acti vated receptor c respectively. A dual peroxisome proliferator-activated receptor model has also been developed, and it indicates the structural features required for the design of ligands with dual peroxisome proliferator-activated receptor activity. These quantitative structure–activity relationship models show the importance of the descriptors here introduced in the prediction and interpretation of the compounds affinity and selectivity.
- Study on the cyclization of 6-arylethynylpyrimidine-5-carbaldehydes with tert-butylamine: microwave versus thermal preparation of pyrido[4,3-d]pyrimidinesPublication . Cikotiene, Inga; Kairys, Visvaldas; Buksnaitiene, Rita; Morkunas, Marius; Rudys, Simonas; Brukstus, Algirdas; Fernandes, Miguel X.Thermal and microwave initiated cyclization of 2,4-disubstituted 6-arylethynylpyrimidine-5-carbalde hydes with tert-butylamine has been studied. A novel high-yielding preparation of 2,4-disubstituted 7- arylpyrido[4,3-d]pyrimidines has been developed. The intermediate compounds were isolated and possible mechanism of the reactions is discussed.
- Evaluation of the substrate envelope hypothesis for inhibitors of HIV-1 proteasePublication . Chellappan, Sripriya; Kairys, Visvaldas; Fernandes, Miguel X.; Schiffer, Celia; Gilson, Michael K.Crystallographic data show that various substrates of HIV protease occupy a remarkably uniform region within the binding site; this region has been termed the substrate envelope. It has been suggested that an inhibitor that fits within the substrate envelope should tend to evade viral resistance because a protease mutation that reduces the affinity of the inhibitor will also tend to reduce the affinity of substrate, and will hence decrease the activity of the enzyme. Accordingly, inhibitors that fit the substrate envelope better should be less susceptible to clinically observed resistant mutations, since these must also allow substrates to bind. The present study describes a quantitative measure of the volume of a bound inhibitor falling outside the substrate envelope, and observes that this quantity correlates with the inhibitor’s losses in affinity to clinically relevant mutants. This measure may thus be use ful as a penalty function in the design of robust HIV protease inhibitors.