Angel C De Dios | PubMed Health

PubMed2004

NMR studies of peptide T, an inhibitor of HIV infectivity, in an aqueous environment.

The synthetic octapeptide peptide T (ASTTTNYT) has been shown to interfere with binding of the HIV-1 envelope glycoprotein gp120 to the chemokine receptor R5, thus preventing viral infection. This study investigated the degree of conformational order of two analogs of peptide T, one biologically active (D-Ala peptide T amide) and one inactive (D-Ala, D-Tyr peptide T amide) using nuclear magnetic resonance (NMR) spectroscopy in an aqueous environment, both in solution and in the frozen solid state. Standard solution NMR techniques such as DQFCOSY, HMQC, ROESY and inversion recovery measurements have been utilized to characterize these peptides. Solid state NMR experiments were likewise employed to study the peptides in a frozen glycerol:water mixture. The NMR results indicate that the monomeric form of both peptide T analogs have considerable conformational heterogeneity. Solid state NMR studies indicate aggregation of D-Ala peptide T, possibly into a beta-sheet structure, at concentrations higher than 10 mM.

Anti-HIV Agents↗

PubMed2002

Solution structures of antimalarial drug-heme complexes.

Paramagnetic metal centers [such as Fe(III) found within ferriprotoporphyrin IX heme (FPIX)] exert through space effects on the relaxation rate of nearby proton spins that depend critically on the metal-proton distance. We have measured these effects for all protons of several antimalarial drugs that bind to FPIX by systematically varying the drug:heme molar ratio in high field NMR experiments. These measurements allow us to determine precise FPIX Fe-drug H distances for the solution structures of noncovalent complexes formed between FPIX mu-oxo dimers and the antimalarial drugs chloroquine (CQ), quinine (QN), and quinidine (QD). Using these distances, we then performed distance restraint calculations to determine the lowest-energy solution structures of these complexes. Structures were solved for neutral, monoprotic (+1), and diprotic (+2) forms of the drugs. Analysis of these structures allows us to visualize for the first time the stereospecific differences between QN and QD binding to FPIX and the differences in populations of QN and QD solution structures upon changes in digestive vacuolar pH for drug resistant malarial parasites [Dzekunov, S. M., et al. (2000) Mol. Biochem. Parasitol. 110, 107-124]. The data indicate a previously unrecognized key role for the CQ aliphatic chain in stabilizing FPIX-CQ complexes, and suggest how lengthening or shortening the chain might perturb stability. We also define FPIX:drug stoichiometries of 2:1 for the complexes formed at physiological FPIX concentrations, in contrast to the 4:1 and 5:1 stoichiometries previously determined at higher FPIX concentrations [Dorn, A., et al. (1998) Biochem. Pharmacol. 55, 727-736]. These atomic resolution antimalarial drug-heme structures should help elucidate how these drugs inhibit formation of hemozoin during metabolism of heme within the malarial parasite Plasmodium falciparum and assist ongoing development of strategies for circumventing antimalarial drug resistance.

Aminoquinolines↗