Biomedical subjects

Y P Mascarenhas

Publications and source records attributed to Y P Mascarenhas.

9 recordsLinked to original sources

PubMed2004

The effect of the cation substitution on the structural and vibrational properties of Cs2NaGaxSc(1-x)F6 solid solution.

Raman scattering and x-ray diffration were used to characterize the structural and vibrational properties of the Cs2NaGaxSc(1-x)F6 solid solutions, for x ranging from 0.0 to 1.0. The Raman spectra, taken at room and low temperature, allow us to follow the phase evolution in detail and indicate the breaking of the local symmetry since low Ga concentration levels. Five compositions were studied by x-ray diffraction: x = 0.0, 0.2, 0.5, 0.8, and 1.0. A cubic space group, Fm3m, was found to x = 0.0 and x = 0.2 and a trigonal one was found to x = 0.5, 0.8, and 1.0. Details of both phases are presented and the correlation between x-ray diffraction and Raman scattering is discussed.

Journal Article↗

PubMed2001

Structural transition and pair formation in Fe3O2BO3.

We observe for the first time a structural phase transition in the oxyborate Fe3O2BO3 which occurs along three leg ladders present in this material. X-ray diffraction shows that this transition at 283 K is associated with a new phase where atomic displacements occur in alternate directions perpendicular to the axis and within the plane of the ladders. Magnetic data show that these displacements lead to the formation of singlet pairs which dissociate close to the structural transition. Anomalies in the transport properties also occur close to 283 K showing that the structural transition is related to a charge ordering phenomenon in a low dimensional structure.

Journal Article↗

PubMed2001

Crystallization and preliminary crystallographic studies of a phospholipase A2 from the venom of the Brazilian snake Bothrops moojeni.

A phospholipase A(2) purified from the venom of the snake Bothrops moojeni has been crystallized by vapour-diffusion techniques in hanging drops at 291 K. The crystals, which were grown in the absence of Ca(2+), belong to the cubic system, space group P432, with unit-cell parameters a = b = c = 91.86 A, and contain one molecule in the asymmetric unit (V(M) = 2.71 A(3) Da(-1)). X-ray diffraction experiments provide data to 2.35 A resolution collected on a rotating-anode home source at cryogenic temperatures. The structure has been solved via molecular-replacement techniques using a single monomer of the crystallographic structure of the phospholipase from the Western diamondback rattlesnake (Crotalus atrox) as a search model.

Animals↗

PubMed1998

Crystallographic and spectroscopic characterization of a molecular hinge: conformational changes in bothropstoxin I, a dimeric Lys49-phospholipase A2 homologue.

Bothropstoxin I (BthTX-I) from the venom of Bothrops jararacussu is a myotoxic phospholipase A2 (PLA2) homologue which, although catalytically inactive due to an Asp49-->Lys substitution, disrupts the integrity of lipid membranes by a Ca2+-independent mechanism. The crystal structures of two dimeric forms of BthTX-I which diffract X-rays to resolutions of 3.1 and 2.1 angstroms have been determined. The monomers in both structures are related by an almost perfect twofold axis of rotation and the dimer interfaces are defined by contacts between the N-terminal alpha-helical regions and the tips of the beta-wings of partner monomers. Significant differences in the relative orientation of the monomers in the two crystal forms results in "open" and "closed" dimer conformations. Spectroscopic investigations of BthTX-I in solution have correlated these conformational differences with changes in the intrinsic fluorescence emission of the single tryptophan residues located at the dimer interface. The possible relevance of this structural transition in the Ca2+-independent membrane damaging activity is discussed.

Animals↗

PubMed1997

Crystallization and preliminary crystallographic data of a neutrophil migration-inducing lectin (KM+) extracted from the seed of Artocarpus integrifolia.

The tetrameric KM+ lectin from the seeds of Artocarpus integrifolia has, when compared to other plant lectins, the singular property of directly inducing neutrophil migration into the peritoneal cavity or into the air pouch of rats. This protein crystals have been grown and they belong to the orthorhombic system with space group C222(1). The unit cell parameters are a = 54.4 A, b = 127.9 A and c = 99.8 A. A native diffraction dataset to 2.8 A was collected and an analysis of the self-rotation function has shown the presence of only one independent non-crystallographic 2-fold axis orthogonal to the crystal b-axis, compatible with a dimer in the asymmetric unit.

Animals↗

PubMed1993

SAXS study of crotapotin at low pH.

The structure of crotapotin, a protein extracted, from the venom of the Crotalus durissus terrificus, in solution at pH = 1.5, was studied by SAXS. The experimental results yield structural parameter values of the molecular radius of gyration Rg = 13.6 A, volume v = 16.2 x 10(3) A3 A3 and maximal dimension Dmax = 46 A. The distance distribution function deduced from the scattering measurements is consistent with an overall molecular shape of an oblate ellipsoid of revolution with asymmetry parameter v = 0.45.

Animals↗

PubMed1992

Structure-function relationship for the highly toxic crotoxin from Crotalus durissus terrificus.

The three-dimensional structure of the highly toxic crotoxin from Crotalus durissus terrificus was modelled based on sequence analysis and the refined structure of calcium-free phospholipase of Crotalus atrox venom. Small-angle x-ray scattering experiments were performed on aqueous solutions of crotoxin. The radial distribution function derived from these scattering experiments and the one calculated from the model structure are in good agreement. Crotoxin consists of a basic and an acidic subunit. The model strongly suggests that the overall folding motif of phospholipases has been preserved in both subunits. The basic domain has an intact active site. The residues that are expected to contact the lipid tails of the phospholipid are different from other phospholipases, but they are all hydrophobic. The acidic domain consists of three independent chains interconnected by disulfide bonds. Compared to other phospholipases the active site for the greater part has been preserved in this domain, but it is not very well shielded from solvent. Most residues normally in contact with the lipid tails of the phospholipid are missing, which might explain the acidic subunit's lack of phospholipase activity. A homology between the third chain of the acidic domain and neurophysins suggests that the acidic domain may act as a chaperone for the basic domain.

Amino Acid Sequence↗

PubMed1990

SAXS study of the snake toxin alpha-crotamine.

alpha-crotamine is a small toxic protein (42 amino acid residues with three disulphide bridges) present in the venom of Crotallus durissus terrificus. Molecular parameters (Rg = 13.7 A, S = 3,000 A2, V = 9,200 A3 and Dmax = 40 A) were derived from SAXS curves obtained from a solution of this protein at pH = 4.5. An excellent agreement between the experimental distance distribution curve and that calculated from a model consisting of two lobes linked by the Cys(18)-Cys(30) disulphide bridge.

Amino Acid Sequence↗

PubMed1985

Saxs study of structure and conformational changes of crotamine.

The radius of gyration of crotamine is determined by the small angle x-ray scattering technique. Several molecular solutions have been studied to correct for concentration effects. The apparent molecular radius of gyration is also determined as a function of pH. An important change between pH 9.5 and 12.5 is attributed to a dominant effect of molecular aggregation.

Crotalid Venoms↗