Biomedical subjects

D Jain

Publications and source records attributed to D Jain.

At least 19 recordsLinked to original sources

PubMed2001

Enhanced binding of a rationally designed peptide ligand of concanavalin a arises from improved geometrical complementarity.

The structural basis of affinity enhancement was addressed by analyzing the interactions between concanavalin A and the carbohydrate-mimicking peptide ligands. Based on the crystal structures of concanavalin A in complex with these peptides [Jain, D., Kaur, K. J., Sundaravadivel, B., and Salunke, D. M. (2000) J. Biol. Chem. 275, 16098-16102; Jain, D., Kaur, K. J., and Salunke, D. M. (2001) Biophys. J. 80, 2912-2921], a high-affinity analogue was designed. This analogue (acetyl-MYWYPY-amide) binds to the lectin with 32-fold enhanced affinity compared to the corresponding precursor peptides. The crystal structure of concanavalin A bound to the designed peptide has been determined. A peptide molecule binds to each of the crystallographically independent monomers of the tetrameric lectin. The four bound peptide molecules exhibit two major conformations both of which are extended. Unlike in the case of other concanavalin A binding peptides, the structural variations within different conformers of this analogue are marginal. It is apparent that the deletion of the structurally variable region of the larger peptides has led to an improved complementarity and increased buried surface area in the case of the designed peptide. The crystal structure also showed the formation of two backbone hydrogen bonds between the ligand and the ligate which were not present in the complexes of the precursor peptides. The observed structural features adequately explain the enhanced binding of the designed analogue.

Concanavalin A↗

PubMed2001

Structure of the induced antibacterial protein from tasar silkworm, Antheraea mylitta. Implications to molecular evolution.

The crystal structure of an antibacterial protein of immune origin (TSWAB), purified from tasar silkworm (Antheraea mylitta) larvae after induction by Escherichia coli infection, has been determined. This is the first insect lysozyme structure and represents induced lysozymes of innate immunity. The core structure of TSWAB is similar to c-type lysozymes and alpha-lactalbumins. However, TSWAB shows significant differences with respect to the other two proteins in the exposed loop regions. The catalytic residues in TSWAB are conserved with respect to the chicken lysozyme, indicating a common mechanism of action. However, differences in the noncatalytic residues in the substrate binding groove imply subtle differences in the specificity and the level of activity. Thus, conformational differences between TSWAB and chicken lysozyme exist, whereas functional mechanisms appear to be similar. On the other hand, alpha-lactalbumins and c-type lysozymes exhibit drastically different functions with conserved molecular conformation. It is evident that a common molecular scaffold is exploited in the three enzymes for apparently different physiological roles. It can be inferred on the basis of the structure-function comparison of these three proteins having common phylogenetic origin that the conformational changes in a protein are minimal during rapid evolution as compared with those in the normal course of evolution.

Amino Acid Sequence↗

PubMed2001

Functional equality in the absence of structural similarity: an added dimension to molecular mimicry.

The crystal structure of meso-tetrasulfonatophenylporphyrin complexed with concanavalin A (ConA) was determined at 1.9 A resolution. Comparison of this structure with that of ConA bound to methyl alpha-d-mannopyranoside provided direct structural evidence of molecular mimicry in the context of ligand receptor binding. The sulfonatophenyl group of meso-tetrasulfonatophenylporphyrin occupies the same binding site on ConA as that of methyl alpha-d-mannopyranoside, a natural ligand. A pair of stacked porphyrin molecules stabilizes the crystal structure by end-to-end cross-linking with ConA resulting in a network similar to that observed upon agglutination of cells by lectins. The porphyrin binds to ConA predominantly through hydrogen bonds and water-mediated interactions. The sandwiched water molecules in the complex play a cementing role, facilitating favorable binding of porphyrin. Seven of the eight hydrogen bonds observed between methyl alpha-d-mannopyranoside and ConA are mimicked by the sulfonatophenyl group of porphyrin after incorporating two water molecules. Thus, the similarity in chemical interactions was manifested in terms of functional mimicry despite the obvious structural dissimilarity between the sugar and the porphyrin.

Binding Sites↗

PubMed2001

Use of paclitaxel in patients with pre-existing cardiomyopathy: a review of our experience.

Cardiac toxicity is frequently the indication for discontinuation of an anthracycline in patients with tumors which remain anthracycline-sensitive. During the 1990s, the most frequently used second-line agents at the Yale Cancer Center (YCC) were the taxanes. The goal of this retrospective analysis was to determine the effect of paclitaxel on cardiac function in patients with cardiomyopathy. YCC outpatient clinic pharmacy order forms were used to identify all patients who had received paclitaxel between December 1995 and November 1997. The clinic records of those patients with a left ventricular ejection fraction (LVEF) of < or = 50% were reviewed to determine the temporal relation between the decreased LVEF and paclitaxel therapy. In addition, clinic records were examined for evidence of prior doxorubicin therapy and history of prior cardiac disease. Between December 1995 and November 1997, 225 patients were treated with paclitaxel in the YCC outpatient clinic. Nine patients had LVEF < or = 50% (mean 37%) prior to initiation of paclitaxel therapy. Six of these patients had equilibrium radionuclide angiocardiographic (ERNA) scans following completion of paclitaxel. In these 6 patients, the mean change in LVEF was +6% (range -3% to +29%). Four patients had improved LVEF following paclitaxel (mean 11%, range 2% to 29%), while 2 patients experienced a decrease in LVEF following paclitaxel treatment (mean 2.5%). The 3 patients who did not have ERNA scans following paclitaxel therapy had no clinical evidence of congestive heart failure. Our experience confirms the results of prior studies that paclitaxel can be safely administered in patients with underlying cardiac dysfunction.

Aged↗

PubMed2001

Immunological implications of structural mimicry between a dodecapeptide and a carbohydrate moiety.

The immunogenicity and antibody cross-reactivity of two chemically different but structurally equivalent molecular mimics were analyzed by presenting them to the immune system in different modes. The observed differences in IgM and IgG responses in terms of cross-reactivity with the mimicking antigen could reflect the differential proliferative abilities of the corresponding B-cells. Modification of the T-cell help, either by using a promiscuous T-cell epitope or by prepriming, led to the shift in the antibody response towards the mimicking epitope. Also, the anti-sugar antibodies could be boosted using a carbohydrate mimicking peptide on cross-immunization. Thus, the carbohydrate-peptide mimicry appears to be a topological quasi-equivalence reflected differently in terms of antibody response during maturation.

Amino Acid Sequence↗

PubMed2001

A unique pitfall in percutaneous coronary angioplasty of in-stent restenosis: guidewire passage out of the stent.

Three cases of in-stent restenosis are narrated, wherein, during balloon angioplasty of the lesion, the guidewire inadvertently exited out of the stent. The forward balloon progress was halted in this region. In the first case, the situation could only be realized when dilatation of a forcefully pushed small balloon avulsed the well-embedded stent. The mishap was averted in the subsequent two cases by reintroduction of a new guidewire. Some suggestions to avoid this eventuality are offered. Though the cases pertain to in-stent restenosis, the observations may be applicable to the procedures in general that entail passage of a guidewire through a stented area.

Aged↗

PubMed2001

Plasticity in protein-peptide recognition: crystal structures of two different peptides bound to concanavalin A.

The structures of concanavalin A (ConA) in complex with two carbohydrate-mimicking peptides, 10-mer (MYWYPYASGS) and 15-mer (RVWYPYGSYLTASGS) have been determined at 2.75 A resolution. In both crystal structures four independent peptide molecules bind to each of the crystallographically independent subunits of ConA tetramer. The peptides exhibit small but significant variability in conformations and interactions while binding to ConA. The crystal structure of another similar peptide, 12-mer (DVFYPYPYASGS), in complex with ConA has been determined (Jain, D., K. J. Kaur, B. Sundaravadivel, and D. M. Salunke. 2000. Structural and functional consequences of peptide-carbohydrate mimicry. J. Biol. Chem. 275:16098-16102). Comparison of the three complexes shows that the peptides bind to ConA at a common binding site, using different contacting residues and interactions depending on their sequence and the local environment at the binding site. The binding is also optimized by corresponding plasticity of the peptide binding site on ConA. The diversity in conformation and interactions observed here are in agreement with the structural leeway concerning plasticity of specific molecular recognition in biological processes. The adaptability of peptide-ConA interactions may also be correlated with the carbohydrate-mimicking property of these peptides.

Concanavalin A↗

PubMed2001

Adenosine inhibits norepinephrine release in the postischemic rat heart: the mechanism of neuronal stunning.

OBJECTIVE: Numerous studies support the concept of impaired postischemic sympathetic neurotransmission in the heart. We hypothesized that postischemic neuronal dysfunction (neuronal stunning) is caused by a transient suppression of exocytotic norepinephrine (NE) release from sympathetic nerve terminals. Furthermore, we assessed the role of presynaptic adenosine-receptors and alpha2-adrenoceptors in neuronal stunning. METHODS AND RESULTS: Exocytotic NE release was induced by two electrical field stimulations (S(1) and S(2)) in isolated perfused rat hearts. S(1) was performed under baseline conditions and S(2) either during or following intervention. Results are expressed as mean S(2)/S(1) ratios+/-S.E.M. Stepwise increase of global ischemic periods (10, 20, and 30 min) induced a progressive suppression of NE release in the postischemic hearts, which was reversible during reperfusion. Both the degree and duration of NE suppression was dependent on the extent of the preceding ischemic period. Following 10-min ischemia complete recovery of NE release was achieved after 5-min reperfusion (1.07+/-0.12), whereas 5-min reperfusion did not restore NE release after 30 min (0.36+/-0.07) of ischemia. The adenosine-receptor antagonists 8-phenyltheophylline (8-PT; non-selective) and 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; adenosine A1-receptor subtype selective) significantly increased NE release after 30-min ischemia and 5-min reperfusion (0.78+/-0.06 and 0.64+/-0.07), while in the same experimental protocol blockade of alpha2-adrenoceptors by yohimbine failed to restore the postischemic release (0.24+/-0.06). In non-ischemic hearts the adenosine analogue R(-)N(6)-(2-phenylisopropyl)adenosine (R-PIA) resulted in a marked suppression of NE release (0.61+/-0.07). The inhibitory effect of R-PIA and 2-chloro-N(6)-cyclopentyladenosine (CCPA; adenosine A1-receptor subtype selective agonist) persisted 5 min after cessation of R-PIA (0.62+/-0.05) and CCPA (0.58+/-0.04). Activation of alpha2-adrenoceptors by 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine (UK 14,304) also caused a reduction of NE release (0.50+/-0.02), but the release increased to control levels 5 min after cessation of UK 14,304 (0.90+/-0.06). CONCLUSIONS: The results establish the phenomenon of neuronal stunning in terms of a postischemic suppression of exocytotic NE release and provide evidence that neuronal stunning is mediated by endogenous adenosine through activation of presynaptic adenosine A1-receptors.

Adenosine↗

PubMed2001

Antiplatelet therapy in acute coronary syndromes without persistent ST-segment elevation.

The treatment of ACS without persistent ST-segment elevation is evolving. Antiplatelet and antithrombin therapy forms the mainstay of medical management. The antiplatelet agents studied can be pharmacologically classified as GP lIb/IIIa receptor antagonists, ADP receptor antagonists, thromboxane inhibitors, and cyclo-oxygenase inhibitors. While aspirin, a cyclo-oxygenase inhibitor, is well entrenched in the treatment (and thus will not be reviewed here), other drugs have been subjects of intense study and large-scale clinical trials in the last decade. In this article we will explore the rationale of using antiplatelet agents, describe the platelet biology and mechanism of action of these drugs, narrate the major phase III trials, and attempt to draw conclusions from the clinical experience. Important trials which have been presented at principal international scientific meetings and which have not yet been published are also cited.

Acute Disease↗

PubMed2001

Annexin-V imaging for noninvasive detection of cardiac allograft rejection.

Heart transplant rejection is characterized pathologically by myocyte necrosis and apoptosis associated with interstitial mononuclear cell infiltration. Any one of these components can be targeted for noninvasive detection of transplant rejection. During apoptotic cell death, phosphatidylserine, a phospholipid that is normally confined to the inner leaflet of cell membrane bilayer, gets exteriorized. Technetium-99m-labeled annexin-V, an endogenous protein that has high affinity for binding to phosphatidylserine, has been administered intravenously for noninvasive identification of apoptotic cell death. In the present study of 18 cardiac allograft recipients, 13 patients had negative and five had positive myocardial uptake of annexin. These latter five demonstrated at least moderate transplant rejection and caspase-3 staining, suggesting apoptosis in their biopsy specimens. This study reveals the clinical feasibility and safety of annexin-V imaging for noninvasive detection of transplant rejection by targeting cell membrane phospholipid alterations that are commonly associated with the process of apoptosis.

Adult↗

PubMed2001

Morphology of isolated colonic crypts.

The traditional paradigm of colonic fluid and electrolyte transport includes a spatial separation of absorptive and secretory processes to surface and crypt cells, respectively. Recent studies of isolated microperfused colonic crypts revealed constitutive Na-dependent fluid absorption while secretion is regulated by one or more neurohumoral agonists. One obvious reason for the difference found in microdissected crypts is their separation from the lamina propria milieu. While it has been shown that isolated crypts are devoid of obvious lamina propria elements, including pericryptal fibroblasts, detailed morphologic information of the content of isolated crypts has been lacking. To characterize the morphology of the isolated crypt, we performed transmission electron microscopy (TEM) and immunofluorescence on microdissected and Ca2+ chelated crypts. Crypt cell type analysis was carried out separately on intact rat colon using light microscopy. TEM revealed a complete lack of either lamina propria cells or extracellular material in crypts isolated by either technique. TEM also revealed a subtle difference between the two isolation methods, with intact basal membranes in microdissected crypts but focal disruption of basal membranes in Ca2+- chelated crypts. Immunofluorescent stains for two basement membrane components (laminin and collagen type IV) revealed the presence of adherent basement membrane only on microdissected crypts; evidence that the plane of separation differs in these two preparations. Crypt cell type analysis on intact rat colon revealed an equal proportion of goblet cells in the right and left colon (approximately 50%) when measuring the middle 70% of the crypts - the area studied during crypt microperfusion. This morphologic analysis will increase our understanding of the observed physiology of isolated colonic crypts.

Animals↗

PubMed2001

A unique complication during coronary angiography: peripheral embolism by selective right coronary engagement--a case report.

"Micro" and "macro" peripheral embolisms during coronary angiography have been described. In all these cases, the aorta or the left heart chambers have been the source of embolus. A patient who during coronary angiography for acute inferior myocardial infarction experienced acute embolism of the left common femoral artery. The source of the embolus was a thrombus-filled right coronary artery, and the precipitating cause was its selective engagement with a diagnostic Judkins right catheter. A brief review of literature is also presented.

Adult↗

PubMed2001

Relationship between intracellular calcium and airway reactivity in guinea pigs.

The present study was carried out to examine the relationship between intracellular free calcium ion concentrations and its regulatory enzymes, sodium potassium adenosine triphosphatase (Na(+),K(+)-ATPase) and calcium adenosine triphosphatase (Ca(2+)-ATPase), with airway reactivity to inhaled histamine in guinea pigs. Forty-nine guinea pigs were included in this study. Of these, 34 animals responded to histamine bronchoprovocation challenge in vivo with a greater than 35% fall in specific airways conductance and were labeled as "reactive," and the remaining 15 were "nonreactive." The dose of histamine producing a 35% fall in specific airways conductance was labeled as ED(35) SGaw. The animals were then sacrificed, and the following biochemical measurements were carried out: intracellular free calcium ion concentrations [Ca(2+)](i) in leukocytes and isolated tracheal smooth muscle cells, activities of Na(+),K(+)-ATPase and Ca(2+)-ATPase in tracheal homogenate, and plasma levels of lysophosphatidylcholine (LPC). Reactive guinea pigs showed significantly higher [Ca(2+)](i) and Na(+),K(+)-ATPase and Ca(2+)-ATPase activities. Airway reactivity (ED(35) SGaw) had significant negative correlation with [Ca(2+)](i), with activities of each of the ATPases and with plasma lysophosphatidylcholine. It is concluded that the level of [Ca(2+)](i) is an important determinant of airway reactivity. Intracellular calcium levels modulate airway response to histamine with higher levels being associated with greater reactivity.

Administration, Inhalation↗

PubMed2001

An unusual complication of metallic balloon shaft fracture during coronary angioplasty.

We describe two cases of metallic balloon catheter shaft fracture, at a site just proximal to the hemostatic Y-adapter, while attempting to push the stent-balloon assembly through a tortuous left circumflex artery. In both instances, the stent carrying the balloon catheter had a stainless-steel hypotube constituting the proximal stiff portion of the shaft. While no inferences pertaining to this design can be made, our cases call for a closer observation. It would probably be prudent to change the catheter or the dilatation strategy once the shaft started buckling.

Angioplasty, Balloon, Coronary↗

PubMed2001

Rotational atherectomy of a stent-jailed septal perforator: a good verdict for the prisoner.

A 61-year-old man is described, in whom percutaneous coronary intervention was done to treat critical ostial stenosis of the first and second septal perforators. The first branch originated from the stented portion of a previously treated left anterior descending artery, while the second branch was distal to the stent. During balloon angioplasty, the balloon catheter could not be delivered to the lesion site in the first branch, although the second branch was easily amenable to balloon dilatation. Rotational atherectomy was done to treat the former. Besides advocating rotational atherectomy as a novel strategy for managing jailed septal perforators, the case presents an insight into the vastly differing interventional situations of stent-jailed branch vis-a-vis de novo branch ostial stenosis.

Atherectomy, Coronary↗

PubMed2000

Liver disease in patients with hereditary hemorrhagic telangiectasia.

BACKGROUND: Hereditary hemorrhagic telangiectasia, or Rendu-Osler-Weber disease, is an autosomal dominant disorder characterized by angiodysplastic lesions (telangiectases and arteriovenous malformations) that affect many organs. Liver involvement in patients with this disease has not been fully characterized. METHODS: We studied the clinical findings and results of hemodynamic, angiographic, and imaging studies in 19 patients with hereditary hemorrhagic telangiectasia and symptomatic liver involvement. RESULTS: We evaluated 14 women and 5 men who ranged in age from 34 to 74 years. All but one of the patients had a hyperdynamic circulation (cardiac index, 4.2 to 7.3 liters per minute per square meter of body-surface area). In eight patients, the clinical findings were consistent with the presence of high-output heart failure. The cardiac index and pulmonary-capillary wedge pressure were elevated in the six patients in whom these measurements were performed. After a median period of 24 months, the condition of three of the eight patients had improved, four were in stable condition with medical therapy, and one had died. Six patients had manifestations of portal hypertension such as ascites or variceal bleeding. The hepatic sinusoidal pressure was elevated in the four patients in whom it was measured. After a median period of 19 months, the condition of two of the six patients had improved, and the other four had died. Five patients had manifestations of biliary disease, such as an elevated alkaline phosphatase level and abnormalities on bile duct imaging. After a median period of 30 months, the condition of two of the five had improved, the condition of one was unchanged, heart failure had developed in one, and one had died after an unsuccessful attempt at liver transplantation. CONCLUSIONS: In patients with hereditary hemorrhagic telangiectasia and symptomatic liver-involvement, the typical clinical presentations include high-output heart failure, portal hypertension, and biliary disease.

Adult↗

PubMed2000

Structural basis of functional mimicry between carbohydrate and peptide ligands of con A.

Crystallographic studies have shown independent binding sites for sugar and peptide ligands of concanavalin A, although they were considered functional mimics based on biochemical experiments. The topological correlation of 12-residue peptide with different carbohydrate ligands of concanavalin A showed similarity between trimannose and the YPY region of the peptide establishing structural mimicry. Molecular docking of trimannose and the YPY motif on the reciprocal binding sites revealed equivalent interactions and energetics implying that the peptide-binding sites may constitute additional sugar-binding subsites of concanavalin A. The binding of a mannose-rich neoglycoprotein with significantly higher affinity compared with that of the methyl alpha-d-mannopyranoside is consistent with this interpretation.

Amino Acid Motifs↗

PubMed2000

Structural and functional consequences of peptide-carbohydrate mimicry. Crystal structure of a carbohydrate-mimicking peptide bound to concanavalin A.

The functional consequences of peptide-carbohydrate mimicry were analyzed on the basis of the crystal structure of concanavalin A (ConA) in complex with a carbohydrate-mimicking peptide, DVFYPYPYASGS. The peptide binds to the non-crystallographically related monomers of two independent dimers of ConA in two different modes, in slightly different conformations, demonstrating structural adaptability in ConA-peptide recognition. In one mode, the peptide has maximum interactions with ConA, and in the other, it shows relatively fewer contacts within this site but significant contacts with the symmetry-related subunit. Neither of the peptide binding sites overlaps with the structurally characterized mannose and trimannose binding sites on ConA. Despite this, the functional mimicry between the peptide and carbohydrate ligands was evident. The peptide-inhibited ConA induced T cell proliferation in a dose-dependent manner. The effect of the designed analogs of the peptide on ConA-induced T cell proliferation and their recognition by the antibody response against alpha-d-mannopyranoside indicate a role for aromatic residues in functional mimicry. Although the functional mimicry was observed between the peptide and carbohydrate moieties, the crystal structure of the ConA-peptide complex revealed that the two peptide binding sites are independent of the methyl alpha-d-mannopyranoside binding site.

Binding Sites↗