Biomedical subjects

Osmar Norberto de Souza

Publications and source records attributed to Osmar Norberto de Souza.

3 recordsLinked to original sources

PubMed2006

A structural model for chorismate synthase from Mycobacterium tuberculosis in complex with coenzyme and substrate.

The enzymes of the shikimate pathway constitute an excellent target for the design of new antibacterial agents; chorismate synthase (CS) catalyzes the last step of this pathway. The prediction of Mycobacterium tuberculosis (MTB) CS three-dimensional structure and the geometric docking of the coenzyme FMN and the substrate EPSP were performed using the crystal structure of CS from Streptococcus pneumoniae as template. Energy minimization of the whole complex showed, as expected, that most of the template interactions are preserved in the MTB structure, except for HIS11, ARG139 and GLN255. However, novel interactions involving ARG111, GLY113 and SER317 were also observed.

Amino Acid Sequence↗

PubMed2005

Molecular dynamics simulation studies of the wild-type, I21V, and I16T mutants of isoniazid-resistant Mycobacterium tuberculosis enoyl reductase (InhA) in complex with NADH: toward the understanding of NADH-InhA different affinities.

The increasing prevalence of tuberculosis in many areas of the world, associated with the rise in drug-resistant Mycobacterium tuberculosis (MTB) strains, presents a major threat to global health. InhA, the enoyl-ACP reductase from MTB, catalyzes the nicotinamide adenine dinucleotide (NADH)-dependent reduction of long-chain trans-2-enoyl-ACP fatty acids, an intermediate in mycolic acid biosynthesis. Mutations in the structural gene for InhA are associated with isoniazid resistance in vivo due to a reduced affinity for NADH, suggesting that the mechanism of drug resistance may be related to specific interactions between enzyme and cofactor within the NADH binding site. To compare the molecular events underlying ligand affinity in the wild-type, I21V, and I16T mutant enzymes and to identify the molecular aspects related to resistance, molecular dynamics simulations of fully solvated NADH-InhA (wild-type and mutants) were performed. Although very flexible, in the wild-type InhA-NADH complex, the NADH molecule keeps its extended conformation firmly bound to the enzyme's binding site. In the mutant complexes, the NADH pyrophosphate moiety undergoes considerable conformational changes, reducing its interactions with its binding site and probably indicating the initial phase of ligand expulsion from the cavity. This study should contribute to our understanding of specific molecular mechanisms of drug resistance, which is central to the design of more potent antimycobacterial agents for controlling tuberculosis.

Amino Acid Sequence↗

PubMed2003

Plasmodium falciparum histidine-rich protein II binds to actin, phosphatidylinositol 4,5-bisphosphate and erythrocyte ghosts in a pH-dependent manner and undergoes coil-to-helix transitions in anionic micelles.

The recombinant histidine-rich protein II (HRPII) from Plasmodium falciparum was shown to bind actin and phosphatidylinositol 4,5-bisphosphate (PIP(2)) in vitro in a pH-dependent manner, very similar to hisactophilin, an actin-binding protein from ameba. Binding of HRPII to actin and PIP(2) occurred at pH 6.0 and 6.5, but not above pH 7.0. Circular dichroism (CD) spectroscopy confirmed that HRPII interacts with actin at pH below 7.0, as judged by the changes induced in the secondary structure of the HRPII/actin mixture. Further CD analysis demonstrated that HRPII adopts a predominantly alpha-helical conformation with anionic micelles of PIP(2) and SDS, but not with neutral micelles of phosphatidylcholine (PC), a feature that is common to many actin-binding proteins involved in cytoskeleton remodeling. Similarly to hisactophilin, a GFP-HRPII fusion protein shuttled from the cytoplasm to the nucleus of HeLa cells as the cellular pH was lowered from 8.0 to 6.0. HeLa cells transfected with the HRPII gene showed increased levels of histidine-rich proteins (HRPs) in the soluble cell fraction at pH 8.0. At pH 6.0, however, HRPs were detected mainly in the insoluble cell fraction. Interestingly, we found that HRPII binds to human erythrocyte membranes at pH 6.0 and 6.5 but not at pH above 7.0. Our results point to remarkable similarities between HRPII, hisactophilin, and actin-binding proteins. Possible roles of the HRPII during Plasmodium infection are discussed in the light of these findings.

Actins↗