Biomedical subjects

G Jayaraman

Publications and source records attributed to G Jayaraman.

At least 19 recordsLinked to original sources

PubMed1998

Correction to flow rate--pressure drop relation in coronary angioplasty: steady streaming effect.

The changed flow pattern of pulsatile blood flow in a catheterized stenosed artery has been studied through a mathematical model. The study takes into account the effect of the movement of the flexible catheter influenced by the pulsatile nature of the flow. The contribution of the steady streaming effect brings into focus the existence of a non-zero mean pressure drop in addition to the one predicted by the linear theory -- a fact overlooked by the previous authors. Thus our results are intended to provide a correction to the mean pressure drop usually calculated by neglecting the non-linear inertia terms. The calculations based on the geometry and the flow conditions representing a real physiological situation as closely as possible suggest that depending upon the values of k (where k is the ratio of the catheter size to vessel size) ranging from 0.2 to 0.5 mean pressure drop increases for any frequency parameter. In addition, it is found that depending upon the material properties, a thin catheter experiencing small oscillations due to the flow conditions is likely to influence in the same way as a thicker catheter which remains fairly stationary inside the artery. The results are sensitive to the shape of the wall geometry and will be different for different wall geometries even if the cross-sectional area reduction at the peak of stenosis is kept the same. Interesting streamline patterns depict distinct boundary layer characteristics both at the artery wall and catheter wall. Finally, the effect of catheterization and its movement on various physiologically important flow characteristics-mean pressure drop, impedance, wall stress is studied for different range of catheter size and frequency parameter.

Angioplasty, Balloon, Coronary↗

PubMed1998

The role of proline in the prevention of aggregation during protein folding in vitro.

Proline effectively inhibits protein aggregation during the refolding of bovine carbonic anhydrase. Other osmolytes used such as glycine and ethylene glycol fail to exhibit the 'aggregation-blockade' role shown by proline. Results of viscosity and ANS fluorescence (1-anilino-8-naphthalene sulphonic acid) experiments suggest that proline at high concentrations forms an ordered supramolecular assembly. Based on these results, it is proposed that proline behaves as a protein folding chaperone due to the formation of an ordered, amphipathic supramolecular assembly. To our knowledge, this is the first report wherein proline is proposed as a protein folding aid.

Anilino Naphthalenesulfonates↗

PubMed1997

Comparison of the hemolytic activity and solution structures of two snake venom cardiotoxin analogues which only differ in their N-terminal amino acid.

Cardiotoxin analogues IV (CTX IV) and II (CTX II) isolated from the venom of Taiwan Cobra (Naja naja atra) differ in their amino acid sequence by a single amino acid at the N-terminal end. Leucine at the N-terminal end in CTX II is replaced by arginine in CTX IV. CTX IV is an unique snake venom cardiotoxin as it is the only cardiotoxin isoform known so far which possesses a positively charged residue at the N-terminal amino acid. All other cardiotoxins have a hydrophobic amino acid (leucine or isoleucine) at their N-terminal end. The aim of the present study is to understand the effect(s) of the presence of a cationic residue on the structure and functional properties of cardiotoxin(s). Comparison of the hemolytic activities of CTX IV and CTX II shows that lytic activity of the former is at least twice as that shown by the latter. Comparison of the solution structures of CTX IV and CTX II using two-dimensional NMR spectroscopy and dynamical simulated annealing technique reveals that the backbone fold of both the toxin isoforms is almost similar. The secondary structural elements in these two cardiotoxin isoforms consist of long, triple-stranded, as well as short, double-stranded, antiparallel beta-sheets. Thermal denaturation experiments showed that the structure of CTX IV is more stable than that of CTX II. Critical analysis of the three-dimensional structures of CTX IV and CTX II reveals the presence of a "cationic" cluster comprising of positively charged residues on the concave side of the CTX IV molecule. Similar clusters consisting of positively charged residues are not found in CTX II. The differential erythrocyte lytic activities of these two cardiotoxins are attributed to the difference(s) in the distribution of the positively charged residues in their three-dimensional structures.

Anilino Naphthalenesulfonates↗

PubMed1997

Solution structure of toxin b, a long neurotoxin from the venom of the king cobra (Ophiophagus hannah).

The solution structure of toxin b, a long neurotoxin (73 amino acids and 5 disulfides) from the venom of Ophiophagus hannah (king cobra), has been determined using 1H NMR and dynamical simulated annealing techniques. The structures were calculated using 485 distance constraints and 52 dihedral angle restraints. The 21 structures that were obtained satisfy the experimental restraints and possess good nonbonded contacts. Analysis of the converged structures revealed that the protein consists of a core region from which three finger-like loops extend outwards. The regular secondary structure in toxin b includes a double and a triple stranded antiparallel beta sheet. Comparison with the solution structures of other long neurotoxins reveals that although the structure of toxin b is similar to those of previously reported long neurotoxins, clear local structural differences are observed in regions proposed to be involved in binding to the acetylcholine receptor. A positively charged cluster is found in the C-terminal tail, in Loop III, and in the tip of Loop II. This cationic cluster could be crucial for the binding of the long neurotoxins to the acetylcholine receptor.

Amino Acid Sequence↗

PubMed1997

Characterization of a partially structured state in an all-beta-sheet protein.

Cardiotoxin analogue III (CTX III) is a low-molecular-mass all-beta-sheet protein isolated from the Taiwan cobra (Naja naja atra) venom. A stable partially structured state similar to the "molten globule' state has been identified for CTX III in a 3% (w/v) solution of 2,2,2-trichloroacetic acid at 298 K. This stable state has been structurally characterized using a variety of techniques such as CD, 1-anilinonaphthalene-8-sulphonate fluorescence binding, Fourier transform IR and two-dimensional NMR spectroscopy techniques. Direct assignment of the homonuclear two-dimensional NMR spectra of the protein in 3% trichloroacetic acid showed that drastic structural perturbation had not taken place in the protein and that the 'intermediate' state retained a significant portion of the native secondary-structural interactions. It is found that about 65% of the native beta-sheet structural contacts are maintained in the partially structured state of CTX III in 3% trichloroacetic acid.

Circular Dichroism↗

PubMed1997

Understanding utero-placental blood flow in normal and hypertensive pregnancy through a mathematical model.

Normal development of utero-placental circulation is crucial not only for the survival and growth of the fetus in utero, but also for maternal well-being. Any disturbance or abnormality may reflect underlying pathology. Geometric conversion of a pre-pregnant spiral vessel into a divergent low-resistance vessel is believed to be responsible for the increased utero-placental blood flow in normal pregnancy. Known biomedical investigative techniques have failed to explain many such underlying haemodynamic changes taking place in the utero-placental system. Therefore, proper understanding of the system using a mathematical model has been found to be useful. The physiological fluid dynamic study is the first in this branch of physiology. Abnormal pressure gradient, axial velocity, volume flow and shear rate are obtained for various slowly changing geometries such as, tapering, divergence, local constrictions and sinusoidal tube for low Womersley parameters. The model can explain many enhanced patho-physiological changes, such as persistence or the appearance of local constriction in the utero-placental vessels. Such pathological changes are considered to be responsible for very high utero-placental resistance, leading to blood flow insufficiency in pre-eclampsia or intra-uterine growth retardations. It is believed that these changes may be caused by low shear rate on the pre-existing deranged or abnormal endothelium. Furthermore, this derangement is caused by an abnormal proliferation of either spiral vessels or the invading non-villous trophoblasts. Doppler flow study can explain and validate some of the theoretically derived flow velocity results. The study opens up a new area of research into utero-placental physiological fluid dynamics.

Computer Simulation↗

PubMed1997

The mechanism of 2,2,2-trichloroacetic acid-induced protein precipitation.

The mechanism of 2,2,2-trichloroacetic acid (TCA)-induced precipitation of proteins is studied. The TCA-induced protein precipitation curves are observed to be U-shaped. It is bound that the protein-precipitate-inducing effects of TCA are due to the three chloro groups in the molecule. Using cardiotoxin III (CTX III) isolated from the Taiwan cobra (Naja naja atra), as a model protein, we attempt to understand the molecular basis for the TCA-induced effects. Employing circular dichroism, proton-deuterium exchange in conjunction with conventional 2D NMR techniques, and 1-anilino naphthalene-8-sulfonate-binding experiments, we demonstrate that CTX III is in a partially structured state similar to the 'A state' in 3% w/v TCA. It is postulated that the formation of this 'sticky' partial structured 'A state' in the TCA-induced unfolding pathway is responsible for the acid-induced protein precipitation.

Chemical Precipitation↗

PubMed1997

Snake venom cardiotoxins-structure, dynamics, function and folding.

Snake cardiotoxins are highly basic (pI > 10) small molecular weight (approximately 6.5 kDa), all beta-sheet proteins. They exhibit a broad spectrum of interesting biological activities. The secondary structural elements in these toxins include antiparallel double and triple stranded beta-sheets. The three dimensional structures of these toxins reveal an unique asymmetric distribution of the hydrophobic and hydrophilic amino acids. The 3D structures of closely related snake venom toxins such as neurotoxins and cardiotoxin-like basic proteins (CLBP) fail to show similar pattern(s) in the distribution of polar and nonpolar residues. Recently, many novel biological activities have been reported for cardiotoxins. However, to-date, there is no clear structure-function correlation(s) available for snake venom cardiotoxins. The aim of this comprehensive review is to summarize and critically evaluate the progress in research on the structure, dynamics, function and folding aspects of snake venom cardiotoxins.

Amino Acid Sequence↗

PubMed1997

Proline is a protein solubilizing solute.

The effect of proline on the prevention of trichloroacetic acid (TCA)-induced protein precipitation is studied. It is found that proline at high concentrations (> 4.0 M) completely prevents TCA-induced precipitation of hen egg white lysozyme. Other osmolytes such as ethylene glycol, glycerol and sucrose fail to prevent the TCA-induced precipitation of lysozyme. Viscosity and 1-anilino-8-naphthalene sulphonic acid binding experiments suggest that proline at high concentration forms an ordered supramolecular assembly. Proline is shown to increase the solubility of protein due to formation of such higher order assemblies. A model of the supra-molecular assembly of proline is proposed and a possible in vivo role of the increased levels of proline under water stress is discussed.

Animals↗

PubMed1997

A comparison of fixation screws for the scaphoid during application of cyclical bending loads.

UNLABELLED: Matched pairs of scaphoids from cadavera were stressed with ramped intensity cyclical bending loads after osteotomy and fixation of one scaphoid with a Herbert screw and fixation of the other with an AO 3.5-millimeter cannulated screw, a Herbert-Whipple screw, an Acutrak cannulated screw, or a Universal Compression screw. The AO screw, Acutrak screw, and Herbert-Whipple screw demonstrated superior resistance to cyclical bending loads compared with the Herbert screw. The Universal Compression screw did not provide better fixation than the Herbert screw because of fractures that occurred at the time of insertion. The AO screw and the Herbert screw were then tested in a separate setup in which a segment of volar cortex had been removed in addition to the simple osteotomy. The loss of volar cortex greatly diminished the quality of the fixation provided by both of the screws during application of ramped intensity cyclical bending loads. CLINICAL RELEVANCE: A fixation device in the scaphoid must be able to withstand the stresses that are placed on the scaphoid as a result of its position spanning the proximal and distal carpal rows. Also, because of the prolonged time required for healing of fractures or non-unions of the scaphoid, the device must be able to withstand many such cycles of stress. The present study demonstrates that commonly used screws for fixation of the scaphoid vary significantly (p < 0.005) in their ability to resist cyclical bending loads.

Biomechanical Phenomena↗

PubMed1997

A measurement of anterior tibial displacement in the closed and open kinetic chain.

Anterior displacement of the tibia during knee extension movement has been identified as a possible factor in anterior cruciate ligament (ACL) reconstruction failure due to the increased stress placed on the graft, leading to a creep response in the healing graft. Nineteen healthy subjects with a unilateral ACL deficiency were evaluated in an open and closed kinetic chain. A KT-1000 was used to measure anterior displacement of the tibia on the femur during isometric open and closed kinetic chain exercise at 30 and 60 degrees. An analysis of variance for repeated measures followed by Newman-Keuls multiple comparison tests were performed to determine the differences between the open and closed kinetic chain for the involved and uninvolved knee. Statistically significant differences were found when comparing the amount of anterior displacement between the open and closed kinetic chain for the involved and uninvolved knee at 30 and 60 degrees. Clinicians utilizing isometric exercise in rehabilitation of the anterior-cruciate-deficient and the anterior-cruciate-reconstructed patient should be aware of the increased amount of anterior tibial displacement when comparing open and closed kinetic chain exercise.

Adult↗

PubMed1996

Effect of chaotropic denaturant on the binding of 1-anilino-8-naphthalene sulfonic acid to proteins.

1-Anilino-8-naphthalene sulfonic acid (ANS), a hydrophobic dye, is widely used to monitor conformational changes occurring in proteins during their folding/unfolding. Using cardiotoxin III (whose conformation remains unperturbed even in 6 M urea) from the Taiwan Cobra (Naja naja atra) venom, it is demonstrated that chaotropic denaturant such as urea directly competes with the interaction between ANS and the protein. The results presented in this report, in our opinion, has significant implication(s) in the area of protein folding, arising out of ANS binding experiments.

Anilino Naphthalenesulfonates↗

PubMed1996

2,2,2-Trifluoroethanol induces helical conformation in an all beta-sheet protein.

The effect of 2,2,2-trifluoroethanol (TFE) on the structure of an all beta-sheet protein, cardiotoxin analogue II (CTX II), from the Taiwan cobra (Naja naja atra) is studied. Using circular dichroism studies, it is found that higher concentrations of TFE induced a structural transition from beta-sheet to alpha-helix, both in the native state (nCTX II) and in denatured but not disulfide reduced CTX II (dCTX II) samples. The beta-sheet to alpha-helix conversion is shown to be cooperative. However, in denatured and reduced CTX II (rCTX II), a TFE transforms a portion(s) of the protein backbone a random coil to an alpha-helical conformation. Based on the solution structure of CTX II and the physical property of TFE, a possible mechanism for the observed backbone structural transitions induced by TFE is discussed. The results described in this paper question the significance of the structure of the "molten globule" intermediate(s) obtained in organic solvents such as TFE.

Amino Acid Sequence↗

PubMed1996

Repression of a matrix metalloprotease gene by E1A correlates with its ability to bind to cell type-specific transcription factor AP-2.

Adenovirus E1A 243-amino acid protein can repress a variety of enhancer -linked viral and cellular promoters. This repression is presumed to be mediated by its interaction with and sequestration of p3OO, a transcriptional coactivator. Type IV 72-kDa collagenase is one of the matrix metalloproteases that has been implicated in differentiation, development, angiogenesis, and tumor metastasis. We show here that the cell type-specific transcription factor AP-2 is an important transcription factor for the activation of the type IV 72-kDa collagenase promoter and that adenovirus E1A 243-amino acid protein represses this promoter by targeting AP-2. Glutathione S-transferase-affinity chromatography studies show that the E1A protein interacts with the DNA binding/dimerization region of AP-2 and that the N-terminal amino acids of E1A protein are required for this interaction. Further, E1A deletion mutants which do not bind to p3OO can repress this collagenase promoter as efficiently as the wildtype E1A protein. Because the AP-2 element is present in a variety of viral and cellular enhancers which are repressed by E1A, these studies suggest that E1A protein can repress cellular and viral promoter/enhancers by forming a complex with cellular transcription factors and that this repression mechanism may be independent of its interaction with p3OO.

Adenovirus E1A Proteins↗

PubMed1996

Effect of pressure on transmural fluid flow in different de-endothelialised arteries.

The effect of pressure on filtration across different de-endothelialised arteries has been studied experimentally, and the existing theoretical model is validated. Segments of different arteries are excised, de-endothelialised and cannulated. Bovine serum albumin Krebs solution is used as perfusate. Transmural water flux is measured by following the movement of an air bubble in a calibrated capillary, which connects the artery to a pressure reservoir; the pressure of which is varied. The hydraulic conductivity Lp is calculated from the flux values. Using available experimental parameters in the case of the thoracic and abdominal aorta, a theoretical model is validated using the experimental results. As the elastic constant for the carotid artery is not available, the theoretical model is used to calculate the elastic constant at different transmural pressures. The values calculated are in the range -4.9 x 10(-8) to -5.7 x 10(-9) cm2 dyne-1 between 50 and 135 mm Hg. Both theoretical and experimental results show a decrease in Lp values with an increase in transmural pressure for the thoracic and abdominal aorta, whereas a different trend is observed in the case of the carotid artery. The Lp values increase at 90 mm Hg, as compared with 50 mm Hg, and with a further increase in transmural pressure the values decrease.

Animals↗

PubMed1996

Estimation of increased flow resistance in a narrow catheterized artery--a theoretical model.

The changed flow pattern in a narrow catheterized artery is studied and an estimate of the increased flow resistance is made. The anomalous behaviour of blood in small blood vessels has been taken into account by modelling blood as a Casson fluid possessing some finite yield stress. Both the cases of steady and pulsatile flow situations are studied. The pulsatile flow is analysed by considering the pressure gradient as a periodic function of time with small inertial effects. The resulting quasi-steady non-linear coupled implicit system of differential equations governing the flow are solved using a perturbation analysis, where it is assumed that the Womersley frequently parameter is small (alpha < 1) which is reasonable for physiological situations in small blood vessels as well as in coronary arteries. The effect of pulsatility, catheter radius and yield stress of the fluid on the yield plane locations, velocity distribution, flow rate, shear stress and frictional resistance are investigated. Because of the yield stress theta, two yield surfaces are found to be located in the flow field. Depending on the ration kappa (catheter size/vessel size) ranging from 0.3 to 0.7 (which is widely used in coronary angioplasty procedures), the frictional resistance to flow in large blood vessels, where the effect of yield stress can be neglected (i.e. theta = 0), increases by a factory ranging from 3 to 33. In small blood vessels with the same range of catheter size and an unit pressure gradient, frictional resistance increase was by a factor of 7-21 when theta = 0.05 and 11-294 when theta = 0.1. For small values of kappa and theta, the frictional resistance increased to several hundred times thus implying that the combined effect of increased catheter radius and yield stress is to obstruct the fluid movement considerably.

Animals↗

PubMed1996

Thermal denaturation of an all beta-sheet protein--identification of a stable partially structured intermediate at high temperature.

The thermal unfolding of an all beta-sheet protein, cardiotoxin analogue III, from the Taiwan Cobra (Naja naja atra) is studied at pH 2.0, 4.0 and 6.0. At pH 4.0, using circular dichroism and 1-anilino naphthalene-8-sulphonic acid (ANS) fluorescence binding studies, a stable partially structured intermediate is detected at 90 degrees C.

Anilino Naphthalenesulfonates↗

PubMed1996

Induction of helical conformation in all beta-sheet proteins by trifluoroethanol.

The effect of 2,2,2-Trifluoroethanol (TFE) on the structure of five all beta-sheet proteins, isolated from the venom of the Taiwan cobra (Naja naja atra), is studied. In all the toxins used, it is observed that significant amount of alpha-helix is induced at higher concentrations of TFE. In all these proteins, the induction of helical conformation and disruption of the tertiary structure seem to occur simultaneously. The structural transitions induced by TFE in reduced and denatured protein appear to be different from those observed in the native protein(s). In our opinion, the findings reported herein could have significant implications on research in the area of protein folding.

Circular Dichroism↗