Biomedical subjects

K Subramanian

Publications and source records attributed to K Subramanian.

At least 19 recordsLinked to original sources

PubMed2001

Cosmic microwave background polarization signals from tangled magnetic fields.

Tangled, primordial cosmic magnetic fields create small rotational velocity perturbations on the last scattering surface of the cosmic microwave background radiation. For fields which redshift to a present value of B0 = 3 x 10(-9) G, these vector modes are shown to generate polarization anisotropies of order 0.1-4 microK on small angular scales (500<l<2000), assuming delta function or a power law spectra with n = -1. About 200 times larger signals result for n = 2 spectra. Unlike inflation generated, scalar modes, these signals are dominated by the odd parity, B-type polarization, which could help in their detection.

Journal Article↗

PubMed2001

Sterically stabilized polyplex: ligand-mediated activity.

Synthetic vectors have been considered as a safer and more versatile alternative to viral-based gene delivery systems. A variety of very simple synthetic vector systems, e.g., cationic lipid- and polymer-complexed plasmid DNA have activity in vivo but it appears to be mediated by non-specific electrostatic interactions limiting targeting. In order to avoid these problems, we designed a sterically stabilized layered colloidal system. The steric polymer coating reduces non-specific interactions. We have synthesized a PEG conjugate of PEI that complexes DNA to form small, stable colloids with a steric polymer coat on their surface. The polymer enhances colloidal stability and reduces non-specific binding and toxicity. It also renders the complex inactive presumably due to reduced binding. Ligands are then appended to the distal end of the steric polymer to restore cell binding and expression at target cells. We prepared conjugates with RGD peptide ligands appended to the distal end of the steric polymer. The resulting conjugates also form complexes but with ligands exposed on their surface restoring binding and activity. Labeled oligonucleotides and DNA were used to measure intracellular distribution. Oligonucleotides are found localized in the nucleus, whereas the labeled plasmid DNA remained in the cytoplasm. Import of plasmid DNA into the nucleus appears to be very inefficient yet sufficient for expression.

Chemical Phenomena↗

PubMed2000

The use of silicon microfabrication technology in painless blood glucose monitoring.

A unique minimally invasive system for painless blood testing is now being commercialized for measurement of blood glucose concentration by diabetics. The novel component of this system, a consumable microsampling and assay device, consists of a tough, flexible silicon microneedle comparable in cross-section to a human hair integrated with a silicon microcuvette. This microneedle is capable of reliably taking a very small sample of whole blood completely painlessly, unlike sticks with the much larger metal lancet that must be used in all other current systems. The device permits a one-step process that avoids the need to transfer blood from a skin puncture to a test strip, thus minimizing blood required and possible mess. The small hand-held instrument containing the consumable is touched to the skin of the arm or any other part of the body, not necessarily the tip of the finger, and held there for one second. During this time, the microneedle is advanced and then withdrawn under microprocessor control, puncturing the skin and drawing less than 200 nanoliters of blood into the microcuvette, where the assay is performed automatically. The instrument calculates the blood glucose concentration, displays the result, and holds it in memory for recall. The consumable is produced by silicon microelectromechanical systems technology and can be produced in high volume at low unit cost. This technology shows promise of being extended to other analytes and to continuous monitoring.

Blood Glucose↗

PubMed2000

The nature of social work services in a large public medical center serving an impoverished multicultural population.

The purpose of this paper is to describe the nature of social work services in a large public medical center serving an impoverished multicultural population. This monitoring evaluation was developed and conducted within the context of a research collaboration between a School of Social Work and a team of clinical workers, supervisors, and administrators from the social work department of the medical center. The paper includes a description of the development of the assessment instrument as well as the findings, including the categories of sociodemographics, assessments, and services delivered by medical social workers. Conclusions emphasize the degree of anxiety and depression in the patients and their families and the need for clinical social workers to be skilled in the multicultural assessment and treatment of these problems. This need is then put into the context of the current health care climate.

Adolescent↗

PubMed2000

Genetic testing for breast and ovarian cancer: implications for life insurance.

As the science of genetic testing progresses, the debate surrounding the uses of genetic information intensifies. In February, President Clinton signed an executive order prohibiting federal agencies from using such information to make hiring, promotion, or placement decisions. Concerns about privacy and discrimination have led many states to propose or enact statutes that prohibit health insurers from using genetic test results in their underwriting decisions. However, few statutes address access to these results by the life insurance industry. This Issue Brief summarizes the current debate on whether life insurers should have access to genetic testing information for breast and ovarian cancer, and provides actuarial insight into the potential effect of such testing on the voluntary term insurance market.

Breast Neoplasms↗

PubMed1998

CaMKIIbeta functions as an F-actin targeting module that localizes CaMKIIalpha/beta heterooligomers to dendritic spines.

Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a serine/threonine protein kinase that regulates long-term potentiation and other forms of neuronal plasticity. Functional differences between the neuronal CaMKIIalpha and CaMKIIbeta isoforms are not yet known. Here, we use green fluorescent protein-tagged (GFP-tagged) CaMKII isoforms and show that CaMKIIbeta is bound to F-actin in dendritic spines and cell cortex while CaMKIIalpha is largely a cytosolic enzyme. When expressed together, the two isoforms form large heterooligomers, and a small fraction of CaMKIIbeta is sufficient to dock the predominant CaMKIIalpha to the actin cytoskeleton. Thus, CaMKIIbeta functions as a targeting module that localizes a much larger number of CaMKIIalpha isozymes to synaptic and cytoskeletal sites of action.

3T3 Cells↗

PubMed1998

Enhancement of aquareovirus infectivity by treatment with proteases: mechanism of action.

The effects of protease digestion on the polypeptide composition and on the infectivity of striped bass virus, an aquareovirus, were examined. Both trypsin and chymotrypsin enhanced the infectivity of the virus. Enhancement of infectivity was correlated with the digestion of the outer capsid protein, VP7. These studies support the assertion that VP7 is the outermost capsid protein and suggest that VP4 and VP5 are exposed on the outer surface of infectious particles. The possible role of VP7 in the variation in virulence observed among aquareovirus isolates is discussed.

Animals↗

PubMed1997

Prenylation-dependent association of Ki-Ras with microtubules. Evidence for a role in subcellular trafficking.

We recently identified a prenyl peptide-binding protein in microsomal membranes from bovine brain (Thissen, J. A., and Casey, P. J. (1993) J. Biol. Chem. 268, 13780-13783). Through a variety of approaches, this binding protein has been identified as the cytoskeletal protein tubulin. Prenyl peptides bind to purified tubulin with a Kd of 40 nM and also bind to tubulin polymerized into microtubules. Microtubule affinity chromatography of extracts from cells in which the prenyl protein pool was metabolically labeled revealed that prenyl proteins bound to the immobilized microtubules; one, a 24-kDa protein, was tentatively identified as a GTP-binding protein. Of several prenylated GTP-binding proteins tested, including Ki-Ras4B, Ha-Ras, RhoB, RhoA, and Rap1B, only Ki-Ras was found to bind significantly to microtubules, and this was in a prenylation-dependent fashion. A potential significance of the interaction of Ki-Ras4B with microtubules was indicated from analysis of the localization of newly synthesized Ki-Ras4B and Ha-Ras, each tagged with green fluorescence protein (GFP). Treatment of NIH-3T3 cells expressing GFP-Ki-Ras with Taxol (paclitaxel) resulted in accumulation of the expressed protein in intracellular locations, whereas in control cells the protein was correctly targeted to the plasma membrane. Importantly, such treatment with paclitaxel did not affect the cellular localization of expressed GFP-Ha-Ras. These results indicate that an intact microtubule network may be directly involved in Ki-Ras processing and/or targeting and provide direct evidence for a physiological distinction between Ki-Ras and Ha-Ras in cells. Additionally, the finding that paclitaxel treatment of cells disrupts Ki-Ras trafficking suggests an additional mechanism for the anti-proliferative effects of this drug.

Animals↗

PubMed1997

Calcium-induced restructuring of nuclear envelope and endoplasmic reticulum calcium stores.

The spatial organization of endoplasmic reticulum (ER) and nuclear envelope (NE) calcium stores is important for the regulation of localized calcium signals and sustained calcium gradients. Here, we have used a lumenal GFP fusion protein and shown that, in resting cells, large molecules can rapidly diffuse across the cell within the lumenal storage space defined by the ER and NE membranes. Increases in cytosolic calcium concentration reversibly fragmented ER tubules and prevented lumenal diffusion. However, the integrity of the NE was maintained, and a significant fraction of NE lumenal protein accumulated in an NE-associated vesicle. These dynamic properties of ER-NE calcium stores provide insights into the spatiotemporal control of calcium signaling.

3T3 Cells↗

PubMed1997

Cloning and sequence analysis of a non-structural gene of an aquareovirus.

The nucleotide and deduced amino acid sequence of genome segment 11 encoding a nonstructural protein of an aquareovirus strain SBR have been determined. Nucleotide sequence analysis showed that the genome segment 11 of SBR virus is 780 nucleotides long and contains a major open reading frame that codes for a polypeptide of 236 amino acids with a predicted molecular weight of 25,504 Da. The second reading frame of genome segment 11 was 480 nucleotides long and codes for a polypeptide of 145 with a predicted molecular weight of 15,715 Da. The genome segment 11 contains 24 nontranslated nucleotides at the 5'-end and 48 nontranslated nucleotides at the 3'-end. This gene codes for two nonstructural polypeptides NS29 and NS15. Comparison of the deduced amino acid sequence of this gene with the published sequences of other members of the family Reoviridae indicated no sequence relatedness.

Amino Acid Sequence↗

PubMed1997

Cloning, sequence analysis and expression of the major outer capsid protein gene of an aquareovirus.

The nucleotide and deduced amino acid sequences of genome segment 10 of aquareovirus strain SBR, encoding the major outer capsid protein (VP7), have been determined. Genome segment 10 of SBR virus is 986 nucleotides long and encodes a polypeptide of 298 amino acids with a predicted molecular mass of 32,430 Da. There are 26 non-translated nucleotides at the 5' end and 66 non-translated nucleotides at the 3' end. Using a recombinant baculovirus system, the VP7 protein of SBR virus was expressed to a high level. The baculovirus-produced VP7 protein was similar both in its size and antigenic properties to the authentic aquareovirus VP7 protein. Antiserum from a rabbit immunized with the baculovirus-produced VP7 protein failed to neutralize the homologous aquareovirus strain. As determined by Western blotting, this antiserum reacted with aquareovirus strains belonging to the same genogroup as SBR virus, but did not react with aquareovirus strains belonging to the other genogroups.

Animals↗

PubMed1997

Identification of a new genogroup of aquareovirus by RNA-RNA hybridization.

The relative mobilities of the 11 dsRNA genomic segments of 22 aquareovirus isolates from fish and shellfish obtained from different geographical areas of the world were compared by PAGE. Using reciprocal RNA-RNA dot blot hybridization, a new sixth genetic group of aquareovirus (genogroup F) was identified. Genogroup A was represented by eight and genogroup B by 12 isolates. The remaining two isolates represented the new sixth genogroup (genogroup F). The genetic relationship of these aquareoviruses with mammalian rotavirus group A (SA 11) was also examined by reciprocal RNA-RNA blot hybridization but none was found under any of the stringency conditions used.

Animals↗

PubMed1996

The structure of aquareovirus shows how the different geometries of the two layers of the capsid are reconciled to provide symmetrical interactions and stabilization.

BACKGROUND: Aquareoviruses are important pathogens of aquatic animals and have severe consequences in aquaculture. These viruses belong to the family Reoviridae. A structural feature common to members of the Reoviridae is a multilayered capsid, formed by several concentric icosahedral shells with different protein compositions. How these proteins, which often are present in unequal stoichiometries, interact between icosahedral layers to stabilize the capsid is not well understood. RESULTS: We have determined the three-dimensional structure of aquareovirus to 23 A resolution using electron cryomicroscopy and computer image analysis. The protein capsid is composed of two structurally distinct icosahedral layers: an outer layer approximately 100 A thick, with incomplete T=13 left-handed symmetry, surrounds an inner layer 600 A in diameter that has T=1 symmetry and is perforated by channels near the fivefold axes. There are 120 subunits, arranged in dimers, in the inner layer, each of which interacts with two of the 600 subunits in the outer layer. A separate set of closely interacting proteins forms the fivefold axes of the virus structure, forming continuous density throughout both layers of the capsid. Comparison of full and empty (lacking RNA) virus structures reveals an RNA shell that lies directly beneath the inner layer. CONCLUSIONS: Our aquareovirus structure displays marked similarity to the mammalian reovirus intermediate subviral particles, suggesting a close evolutionary relationship. However, the noticeable distinction is that aquareovirus lacks the hemagglutinin spike observed in reovirus. The T=1 inner layer organization observed in the aquareovirus appears to be common to other members of the Reoviridae. Such organization may be of fundamental significance in the endogenous transcription of the genome in these viruses.

Animals↗

PubMed1996

The Fc segment of IgE influences the kinetics of dissociation of a symmetrical bivalent ligand from cyclic dimeric complexes.

As part of a systematic effort to determine the features of immunoglobulin E-receptor (IgE-Fc epsilon RI) aggregation that are critical for cellular activation, we used fluorescence to examine the dissociation of a soluble bivalent ligand, N, N'-bis[[epsilon-[(2,4-dinitrophenyl)amino]caproyl]-L-tyrosyl]-L-cystine ((DCT)2-cys), from soluble bivalent IgE and its bivalent F(ab')2 and monovalent Fab' fragments. Cross-linking of Fab' fragments by (DCT)2-cys is limited to linear dimers, and we find that (DCT)2-cys dissociation from Fab' occurs with a single kinetic coefficient [(4.2 +/- 0.6) x 10-3 s-1] that corresponds to the lower of the two kinetic coefficients observed with the bivalent IgE [(4.7 +/- 0.7) x 10-2 s-1 and (4.4 +/- 0.3) x 10-3 s-1]. Similarly, the lower value is obtained for dissociation of (DCT)2-cys that is monovalently bound to IgE after incubation with a large excess of the ligand. (DCT)2-cys can bind to bivalent F(ab')2 fragments and form a variety of linear and cyclic aggregates, similarly to IgE, but, unlike IgE, we find that dissociation occurs with a single kinetic coefficient similar to that observed for Fab'. We find that IgE and its (Fab')2 fragments form highly stable cyclic dimer rings with two (DCT)2-cys. We demonstrate that the kinetic coefficients are independent of enhanced fluorescence quenching observed for bound sites in cyclic dimers. Together, the results show that the rate constant for breaking a linear cross-link formed by (DCT)2-cys is the same as that for dissociation of the monovalently bound (DCT)2-cys. Further, they show that opening of a bond in a dimer ring for the F(ab')2 fragment occurs with approximately the same dissociation rate constant as opening a bond in a linear cross-link. This rate constant is about three times smaller than that observed with IgE, suggesting that steric strain is caused by apposed Fc segments in cyclic IgE dimers. Such structural interference may affect the functional consequences of IgE-Fc epsilon RI aggregation on the cell surface.

Animals↗

PubMed1996

Ehretianone, a novel quinonoid xanthene from Ehretia buxifolia with antisnake venom activity.

Ehretianone (1), a new quinonoid xanthene, together with known sterols, was isolated from a MeOH extract of the root bark of Ehretia buxifolia. The structure of ehretianone was elucidated as 7-hydroxy-9a alpha-(3-methylbut-2-enyl)-4a alpha,9 alpha-(2-methylprop-2-enyl)-4a, 9a-dihydro-1,4-dioxoxanthene on the basis of spectroscopic data and X-ray crystallographic analysis. The antisnake venom activity of ehretianone against Echis carinatus venom in mice is also reported.

Animals↗

PubMed1995

Simultaneous cross-linking by two nontriggering bivalent ligands causes synergistic signaling of IgE Fc epsilon RI complexes.

We have used two bivalent ligands that bind IgE to study the relationship between the aggregation of receptors with high affinity for IgE (Fc epsilon RI) and the responses (receptor immobilization, Ca2+ influx, and degranulation) of rat basophilic leukemia (RBL-2H3) cells. One of these is a symmetric bivalent ligand, N,N'-bis[[epsilon-[(2,4-dinitrophenyl)amino]caproyl]-L-tyrosyl]-L- cystine ((DCT)2-cys), which binds specifically to the combining sites of a mAb anti-DNP IgE and efficiently cross-links cell surface IgE, but does not trigger significant degranulation or increases in intracellular Ca2+. Several lines of evidence, including lateral mobility measurements, indicate that this ligand preferentially forms stable cyclic complexes containing two (DCT)2-cys and two IgE. The second ligand is a mAb anti-IgE, B1E3, which causes lateral mobility changes consistent with dimerized IgE-Fc epsilon RI and also does not trigger increases in intracellular Ca2+ or degranulation. The two ligands together trigger robust responses. In the presence of B1E3, (DCT)2-cys causes immobilization of IgE-Fc epsilon RI in a broad concentration range; in a more narrow concentration range, it is a potent stimulant of changes in both degranulation and Ca2+. We have compared the dose-response curves for cellular activation to simulated IgE aggregation curves, i.e., curves that predict the equilibrium IgE aggregate size distribution as a function of the (DCT)2-cys concentration. Our results indicate that maximal cellular activation occurs at a much higher (DCT)2-cys concentration than maximal IgE aggregation. When IgE aggregation is maximal, almost all aggregated IgE is in cyclic dimers. Thus, cyclic dimers appear to be functionally ineffective, even after they have been cross-linked by B1E3. Aggregated IgE-Fc epsilon RI that is effective in stimulating a cellular response may have particular structural or dynamic properties that allow critical interactions for initiating the signaling cascade.

Animals↗

PubMed1995

Spectroscopic studies on the interaction of three partially hydrogenated acridine dyes with calf thymus DNA and their structural comparison.

The interaction of three partially hydrogenated acridine dyes (acridine I, acridine II and acridine III) with calf thymus DNA was studied using spectrophotometric and spectrofluorometric methods. This paper presents the evidence for the formation of complexes between acridine I, II and III with calf thymus DNA. From the results of this studies various binding parameters were evaluated. The binding constant for acridine I and acridine III ranged from 2.1 to 4.4 x 10(5) M-1 for the P/D ratio from 4.29 to 0.56 while for acridine II this constant increased from 0.78 to 2.26 x 10(5) M-1 for the P/D ratio 12 to 2.38 and decreased to 1.47 at P/D ratio 1.34. The Scatchard analysis indicated a cooperative binding of acridine II to calf thymus DNA as compared to acridine I and III. A red shift in the visible absorption bands for dye DNA complexes (for acridine I = 8, acridine II = 7, and acridine III = 9 nm) suggested an electronically coupled interaction mode for the dyes. It is concluded that acridine II interacted stronger with calf thymus DNA than acridine I or III. The results are interpreted in terms of their crystal structures and also with the already reported DNA binder structures.

Acridines↗

PubMed1995

Characterization of 2 aquareovirus proteins.

The protein products of aquareovirus genome segments 10 and 11 were investigated. The genome segment 10 encodes the major outer capsid protein (VP7) of aquareovirus. The VP7 protein has a molecular weight of 35 kDa and was found to be glycosylated. The electrophoretic mobility of VP7 in SDS-PAGE was unaltered when untreated and deglycosylated proteins were compared, indicating the presence of short oligosaccharide chains. Selective binding of lectins with well-defined sugar specificities suggest that most of the short N-linked carbohydrate chains of VP7 contain galactose residues. Genome segment 11 encoded 2 non-structural proteins (NS29 and NS15). Partial protease mapping indicated that the NS29 and NS15 proteins are derived from initiation of protein synthesis at 2 distinct sites.

Animals↗