Structures of falcipain-2 and falcipain-3 bound to small molecule inhibitors: implications for substrate specificity.

Falcipain-2 and falcipain-3 are critical hemoglobinases of Plasmodium falciparum, the most virulent human malaria parasite. We have determined the 2.9 A crystal structure of falcipain-2 in complex with the epoxysuccinate E64 and the 2.5 A crystal structure of falcipain-3 in complex with the aldehyde leupeptin. These complexes represent the first crystal structures of plasmodial cysteine proteases with small molecule inhibitors and the first reported crystal structure of falcipain-3. Our structural analyses indicate that the relative shape and flexibility of the S2 pocket are affected by a number of discrete amino acid substitutions. The cumulative effect of subtle differences, including those at "gatekeeper" positions, may explain the observed kinetic differences between these two closely related enzymes

Computational Identification of Uncharacterized Cruzain Binding Sites

Chagas disease, caused by the unicellular parasite Trypanosoma cruzi, claims 50,000 lives annually and is the leading cause of infectious myocarditis in the world. As current antichagastic therapies like nifurtimox and benznidazole are highly toxic, ineffective at parasite eradication, and subject to increasing resistance, novel therapeutics are urgently needed. Cruzain, the major cysteine protease of Trypanosoma cruzi, is one attractive drug target. In the current work, molecular dynamics simulations and a sequence alignment of a non-redundant, unbiased set of peptidase C1 family members are used to identify uncharacterized cruzain binding sites. The two sites identified may serve as targets for future pharmacological intervention

ABSORPTION AND POLARIZED PHOSPHORESCENCE SPECTRA OF SUBSTITUTED s-TRIAZINES.

Author Institution: Central Research Division, American Cyanamid CompanyThe ultraviolet absorption spectra of methyl and phenyl derivatives of s-triazine were measured in both polar and non-polar solvents at room temperature and $77^{\circ}$K. In contrast to s-triazine and the methyl triazines where a low energy ($\sim 37,000 cm.^{-1}$), relatively intense $(\epsilon \sim 700\,1./mole\, cm)n\to \pi^{\ast}$ transition is observed, the phenyl triazines show a very intense $(\epsilon>2.5 \times 10^{4}\, 1./mole\,cm.)n\to \pi^{\ast}$ transition at $\sim 38,500\,cm.^{-1}$ which is very similar to biphenyl and the angular polyphenyls. At $33,000\,cm.^{-1}$ there is an indication of a shoulder which is obscured in alcohol solvent. It is tempting to attribute this weak feature to an $n\to \pi^{\ast}$ transition, but the evidence is not very convicining. The polarization of the phosphorescence of the phenyl derivatives of s-triazine was determined in rigid glass solutions at $77^{\circ}K$, by the method of ``Photoselection''. Excitation spectra of the polarized phosphorescence of these molecules has permitted an unambiguous assignment of the lowest energy singlet transition as an $n\to \pi^{\ast}$ orbital type

Structures of falcipain-2 and falcipain-3 bound to small molecule inhibitors: implications for substrate specificity.

Falcipain-2 and falcipain-3 are critical hemoglobinases of Plasmodium falciparum, the most virulent human malaria parasite. We have determined the 2.9 A crystal structure of falcipain-2 in complex with the epoxysuccinate E64 and the 2.5 A crystal structure of falcipain-3 in complex with the aldehyde leupeptin. These complexes represent the first crystal structures of plasmodial cysteine proteases with small molecule inhibitors and the first reported crystal structure of falcipain-3. Our structural analyses indicate that the relative shape and flexibility of the S2 pocket are affected by a number of discrete amino acid substitutions. The cumulative effect of subtle differences, including those at "gatekeeper" positions, may explain the observed kinetic differences between these two closely related enzymes