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Biomedical subjects

K Gunasekaran

Publications and source records attributed to K Gunasekaran.

At least 37 records · Page 2Linked to original sources
PubMed1999

Effect of bacillus thuringiensis ssp. israelensis on the development of Plasmodium gallinaceum in Aedes aegypti (Diptera: Culicidae).

Adult, female Aedes aegypti, some of which had survived a sublethal dose (LC50) of Bacillus thuringiensis ssp. israelensis (Bti) as larvae, were fed on chickens with gametocytaemia of Plasmodium gallinaceum. Parasite development was monitored by dissecting samples of the mosquitoes immediately after the feed and on days 1, 7 and 9 post-feed, to check for the presence of gametocytes, ookinetes, oocysts and sporozoites, respectively. As the proportions of batches of fed mosquitoes found positive for gametocytes and ookinetes and the density of these parasite stages in the infected flies did not differ significantly between Bti-treated and untreated mosquitoes, ingestion of gametocytes and development of ookinetes did not appear to be affected by Bti exposure. However, the Bti-treated mosquitoes were significantly less likely to carry oocysts and those that were oocyst-positive carried significantly fewer oocysts than the untreated controls, indicating Bti-induced parasite loss during development of oocysts. Consequently, the proportion of mosquitoes with sporozoites was also significantly lower in the treated group. The study shows that mosquitoes surviving Bti treatment did not fully support parasite development. The implication of this effect is discussed in terms of malaria transmission.

Aedes↗
PubMed1998

Conformational interconversions in peptide beta-turns: analysis of turns in proteins and computational estimates of barriers.

The two most important beta-turn features in peptides and proteins are the type I and type II turns, which differ mainly in the orientation of the central peptide unit. Facile conformational interconversion is possible, in principle, by a flip of the central peptide unit. Homologous crystal structures afford an opportunity to structurally characterize both possible conformational states, thus allowing identification of sites that are potentially stereochemically mobile. A representative data set of 250 high-resolution (</=2.0 A), non-homologous protein crystal structures and corresponding variant and homologous entries, obtained from the Brookhaven Protein Data Bank, was examined to identify turns that are assigned different conformational types (type I/type II) in related structures. A total of 55 examples of beta-turns were identified as possible candidates for a stereochemically mobile site. Of the 55 examples, 45 could be classified as a potential site for interconversion between type I and type II beta-turns, while ten correspond to flips from type I' to type II' structures. As a further check, the temperature factors of the central peptide unit carbonyl oxygen atom of the 55 examples were examined. The analysis reveals that the turn assignments are indeed reliable. Examination of the secondary structures at the flanking positions of the flippable beta-turns reveals that seven examples occur in the loop region of beta-hairpins, indicating that the formation of ordered secondary structures on either side of the beta-turn does not preclude local conformational variations. In these beta-turns, Pro (11 examples), Lys (nine examples) and Ser (seven examples) were most often found at the i+1 position. Glycine was found to occur overwhelmingly at position i+2 (28 examples), while Ser (seven examples) and Asn (six examples) were amongst the most frequent residues. Activation energy barriers for the interconversion between type I and type II beta-turns were computed using the peptide models Ac-Pro-Aib-NHMe and Ac-Pro-Gly-NHMe within the framework of the AM1 semi-empirical molecular orbital procedure. In order to have a uniform basis for comparison and to eliminate the distracting influence of the deviation of backbone dihedral angles from that expected for ideal beta-turns, the dihedral angles phii+1 and psii+2 were fixed at the ideal values (phii+1=-60 degrees and psii+2=0 degrees). The other two angles (psii+1 and phii+2) were varied systematically to go from type II to type I beta-turn structures. The computational results suggest that there exists one stereospecific, concerted flip of the central peptide unit involving correlated single bond rotation that can occur with an activation barrier of the order of 3 kcal/mol. The results presented here suggest that conformational variations in beta-turns are observed in protein crystal structures and such changes may be an important dynamic feature in solution.

Models, Chemical↗
PubMed1998

Stereochemical punctuation marks in protein structures: glycine and proline containing helix stop signals.

An analysis on the nature of alpha-helix stop signals has been carried out, using a dataset of 1057 helices identified from 250 high resolution (</=2.0 A), non-homologous, protein crystal structures. The backbone dihedral angles (phi, psi) of the terminating residue (T) were found to cluster either in the left-handed helical region (alphaL: phi=20 degrees to 125 degrees and psi=-45 degrees to 90 degrees ; 469 helices (44%)) or in the extended region (E: phi=-180 degrees to -30 degrees and psi=60 degrees to 180 degrees and -180 degrees to -150 degrees ; 459 helices (43%)) of the Ramachandran map. These two broad categories of helix stop signals, alphaL and E-terminated helices, were further examined for sequence preferences. Gly residues were found to have an overwhelming preference to occur as the "alphaL-terminator (T)" resulting in the classical Schellman motif, with a strong preference for hydrophobic residues at position T-4 and T+1. In the case of E-terminated helices His, Asn, Leu and Phe were found to occur with high propensity at position T. Quite remarkably Pro residues, with single exception, were absent at position T, but had the highest propensity at position T+1. Examination of the frequencies of hydrophobic (h) and polar (p) residues at positions flanking Gly/Pro permitted delineation of exclusive patterns and predictive rules for Gly-terminated helices and Pro-terminated helices. The analysis reveals that Pro residues flanked by polar amino acids have a very strong tendency to terminate helices. Examination of a segment ranging from T-4 to T+3 appeared to be necessary to determine whether helix termination or continuation occur at Gly residues. The two types of helix termination (alphaL, E) signals also differed dramatically in their solvent accessibility. Gly and Pro residues at helix termini appeared to be strongly conserved in homologous sequences.

Forecasting↗
PubMed1998

Efficacy of a Bacillus sphaericus formulation as influenced by the quality of Culex quinquefasciatus breeding waters.

To understand the physico-chemical factors that influence the efficacy of B. sphaericus formulation in the breeding sites of Culex quinquefasciatus, a study was carried out in Mayiladuturai area of Tamil Nadu (India). The factors studied were hydrogen ion concentration (pH), acidity, alkalinity, chlorides, phosphates, total hardness, sulphates, total solids, dissolved solids, suspended solids, nitrate nitrogen, ammoniacal nitrogen, dissolved oxygen, biological oxygen demand (BOD) and chemical oxygen demand (COD). Efficacy of the formulation was assessed in terms of reduction in larval population in the treated habitats. pH of water in the treated sites was around neutral range (mean +/- SD 7.65 +/- 0.23). Phosphate content was low (2.27 +/- 1.34 ppm) whereas chlorides (326.1 +/- 55.8 ppm) and sulphates (38.9 +/- 23.8 ppm) were high. Total hardness ranged from 206 to 462.5 ppm with a mean of 312.1 +/- 80.5 ppm. The chlorides and sulphates, though present in considerable quantity, did not have any influence on the efficacy of B. sphaericus formulation. However, the proportion of insoluble chlorides and sulphates which contribute to total hardness seemed to influence the formulation adversely.

Animals↗
PubMed1997

Beta-hairpins in proteins revisited: lessons for de novo design.

Beta-Hairpins with short connecting loops (1-5 residues) have been identified from a data set of 250 non-homologous, high resolution (< or =2.0 A) protein crystal structures. The conformational preferences of the loop segments have been analyzed with the specific aim of identifying frequently occurring motifs. Type I' and II' beta-turns were found to have a high propensity for occurrence in two residue loops. For three and four residue loops, the major conformational motif in the linking segments is alphaR-alphaR-alphaL (type I beta-turn followed by a residue in a left-handed helical conformation) and alphaR-alphaR-alphaR-alphaL (a pi-turn motif), respectively. The present larger data set confirms the high occurrences of these motifs which have been identified in earlier analyses. In addition to type I' and type II' beta-turns, several examples of type I beta-turn nucleated two residue loop hairpins, in spite of having an opposing sense of twist to that of type I' beta-turn, have also been observed. Examination of these frequently occurring motifs (flanked by extended conformation [beta]) in the data set reveals that the motifs beta-alphaR-alphaR-alphaL-beta and beta-type I'-beta have equal propensity and type II' indeed having highest propensity to nucleate beta-hairpins. The larger number of examples in this study allows the estimation of the specific amino acid preferences for loop positions in two, three and four residue loops. Small polar residues Asn, Asp, Ser, Thr, Gly and Pro in general have a high propensity for the loop positions but they reveal specific positional preferences in these frequently occurring motifs. There are no strong compositional preferences in the strand segments. Amino acid pair correlations across strands also do not show any significant pattern, with the exception of Cys-Cys pairs. Several Cys-Cys pairs have been identified at the non-hydrogen bonded positions of beta-hairpins; as many as six are disulfide bonded pairs. An examination of longer loop length hairpins reveals that the distortions of hairpins nucleated by tight turns (two residues) are much less frequently observed. The results presented in this study provide inputs for the de novo design of consensus loop segments in synthetic hairpins.

Amino Acid Sequence↗
PubMed1997

Development of alginate-based slow release formulation of Bacillus sphaericus for controlling Culex quinquefasciatus.

Seven types of formulations were prepared as granules using the larvicidal factor of Bacillus sphaericus and different concentrations of calcium alginate which was used as matrix to immobilize and entrap the active ingredient (ai). All formulations were tested in disused wells against Culex quinquefasciatus at the rate of 15 kg ai per hectare. Among the seven types tested, the type 2 which contained 5% calcium alginate as immobilizing agent, exhibited the maximum larvicidal activity. Persistent control in breeding was noticed for 8 weeks with this formulation type.

Alginates↗
PubMed1996

Disallowed Ramachandran conformations of amino acid residues in protein structures.

An analysis of the nature and distribution of disallowed Ramachandran conformations of amino acid residues observed in high resolution protein crystal structures has been carried out. A data set consisting of 110 high resolution, non-homologous, protein crystal structures from the Brookhaven Protein Data Bank was examined. The data set consisted of a total of 18,708 non-Gly residues, which were characterized on the basis of their backbone dihedral angles (phi, psi). Residues falling outside the defined "broad allowed limits" on the Ramachandran map were chosen and the reported B-factor value of the alpha-carbon atom was used to further select well defined disallowed conformations. The conformations of the selected 66 disallowed residues clustered in distinct regions of the Ramachandran map indicating that specific phi, psi angle distortions are preferred under compulsions imposed by local constraints. The distribution of various amino acid residues in the disallowed residue data set showed a predominance of small polar/charged residues, with bulky hydrophobic residues being infrequent. As a further check, for all the 66 cases non-hydrogen van der Waals short contacts in the protein structures were evaluated and compared with the ideal "Ala-dipeptide" constructed using disallowed dihedral angle (phi, psi) values. The analysis reveals that short contacts are eliminated in most cases by local distortions of bond angles. An analysis of the conformation of the identified disallowed residues in related protein structures reveals instances of conservation of unusual stereochemistry.

Amino Acids↗
PubMed1996

Efficacy of Bacillus sphaericus in different breeding habitats of Culex quinquefasciatus.

'Spherifix', an alginate based slow release formulation of Bacillus sphaericus was field tested in different types of breeding habitats of Culex quinquefasciatus at the dose of 15 kg ai/ha at bimonthly interval. The efficacy of the formulation was higher in most of the months except in rainy and post-rainy months. The mean percentage reduction +/-SD during the treatment phase of one year was 31.2 +/- 17.9, 50 +/- 29.4, 28.3 +/- 17.6, 30.3 +/- 21.1, 66 +/- 22.5 and 53 +/- 20.4 in larval density and 49 +/- 20.8, 65.1 +/- 26.1, 30.3 +/- 21.9, 59.8 +/- 22.6, 63.1 +/- 21.9 and 47.7 +/- 24.2 in pupal density respectively in cement tanks, cesspools, cesspits, disused wells, unlined drains and cement lined drains. The reduction in immature density was relatively higher in undisturbed, debris free and shallow habitats such as cesspools, unlined drains and cement lined drains. After withdrawal of treatment, the effect of the formulation could be seen for a period of four months.

Animals↗
PubMed1995

Stereochemical analysis of the antigenic tip of the V3 loop peptide of HIV-1 gp120.

A novel multiple turn conformation has been observed for a segment GPGRAFY in the crystal structure of a complex of HIV-1 gp120 V3 loop peptide with the Fab fragment of a neutralizing antibody [Ghiara et al. (1994) Science 264, 82-85]. A structural motif has been defined for the peptide segment, employing idealized backbone conformations characterized by ranges of virtual C alpha torsion angles and bond angles. A search of 122 high-resolution protein crystal structures has permitted identification of 24 examples of similar structural motifs. Two major conformational families have been identified, which differ primarily in the conformation at residue 3. The observed conformation at residue 3 in family 1 is left-handed helical (alpha L) and that in family 2 is right-handed helical (alpha R). Of the 10 examples in family 1, 9 examples have Gly residues at position 3. Of the 12 examples in family 2, 7 examples have Asn/Asp at position 3. Computer modeling of the V3 loop tip sequence using the two backbone conformational families as starting points leads to minimum-energy conformations in which antigenically important side-chains occupy similar spatial arrangements. This stereochemical analysis of the V3 loop tip sequence suggests a rational basis for the design of synthetic analog peptides for use as viral antagonists or synthetic antigens.

Amino Acid Sequence↗
PubMed1994

Reliability of light trap sampling for Anopheles fluviatilis, a vector of malaria.

The utility of light traps for sampling Anopheles fluviatilis, the major malaria vector in the hill tracts of Koraput district, Orissa, was assessed. A modified version of the CDC miniature light trap was used in the study. The data generated from light trap collections were analysed and compared with daytime resting, man-biting and night resting collections carried out in parallel. The number per trap recorded in cattle sheds was significantly higher than that recorded in human dwellings. A similar pattern was observed in hand catches of indoor resting population though the difference was not significant. The density recorded from light traps over time was found to have a significant positive linear association with corresponding indoor (r = 0.625; p = 0.0019) as well as outdoor (r = 0.603; p = 0.0029) diurnal resting densities. The proportion with different gonotrophic stages varied significantly between different types of collections. The age structure of A. fluviatilis did not differ significantly with the types of collection. As the light trap catches reflect seasonal fluctuations in the diurnal resting collections, they can justifiably be used in monitoring the relative density of A. fluviatilis in the place of cumbersome hand catch methods. Other uses of light traps are also discussed.

Animals↗
PubMed1994

Observations on nocturnal activity and man biting habits of malaria vectors, Anopheles fluviatilis, An. annularis and An. culicifacies in the hill tracts of Koraput District, Orissa, India.

Biting and feeding behavior of malaria vectors were studied in nine villages (5 from Jeypore zone and 4 from Malkangiri zone) of Koraput District. Man biting catches comprised of 16 anopheline species including the incriminated vectors of this area: An. fluviatilis, An. annularis and An. culicifacies. An. fluviatilis was predominant and biting of this species recorded indoors throughout the year in both the zones. The period, during which the biting activity peaked, was different between the two zones and consequently the time of peak transmission was also different between the zones. The biting activity was at its peak between 21.00 and 03.00 hours in both the zones. However, in cold season the biting activity peaked in the first quarter of the night in Jeypore zone. The anthropophilic index (AI) of An. fluviatilis was 26.2% in Jeypore and 83.7% in Malkangiri and of An. culicifacies the AI was 0.4% in Jeypore and 7% in Malkangiri. Analysis of gonotrophic stages of night resting females indicated that in Jeypore zone, the majority of An. fluviatilis female left indoors for outdoor resting before the completion of gonotrophic cycle, but in Malkangiri, the females remained indoors till the end of the gonotrophic cycle. The presence of full-fed females in night resting catches in Jeypore village further suggested that the females do not leave the house immediately after taking blood meal but rest for some time.

Altitude↗
PubMed1994

Age composition, natural survival and population growth of Anopheles fluviatilis James, 1902, the major malaria vector in the endemic belt of Koraput District, Orissa, India.

The population growth of Anopheles fluviatilis, the major malaria vector, was studied in the hill tracts of Koraput district. Immature duration ranged from 11 to 14 days (mean = 12.42 +/- 0.99) in rainy and 12 to 17 days (mean = 14.78 +/- 1.64) in cold season. The probability of immature survival through different developmental stages was maximal in ponds. Daily survival rate of adults fluctuated between 0.55 and 0.92. The net reproductive rate (Ro) was estimated to be 3.0200 for cold and 0.6486 for rainy season. The mean generation time (T) was slightly longer in cold season (22.32 days) than rainy season (21.24 days). The intrinsic rate of population increase (rm) and consequently the finite rate of increase (lambda) were estimated for cold and rainy seasons. Population growth based on adult resting density was also assessed for different seasons.

Age Distribution↗
PubMed1993

A note on the impact of mud plastering on the efficacy of DDT residual spraying in tribal villages of Koraput District, Orissa State.

A field trial was undertaken to study the impact of mud plastering on the efficacy of DDT spraying in two villages in Koraput district. In Maliguda village, where 95 per cent spray coverage was achieved and the spray surfaces were retained without mud plastering up to 29 and 60 days in first and second round of the spray respectively, malaria cases reduced by 72 per cent after spray for a period of two months. In Dandabedha village with 85 per cent coverage and immediate mud plastering, the malaria cases reduced by 49 per cent. It is concluded that even though mud plastering reduces the effectiveness of the residual spraying to a certain extent, timely spray and better coverage with correct dosage can still effectively reduce the malaria incidence.

Aedes↗
PubMed1993

Studies on dispersal of malaria vectors in a hilly tract of Koraput District, Orissa State, India.

Dispersal of malaria vectors was studied in a hilltop village in Koraput, a highly malarious district of Orissa. Immatures from terraced stream beds and day-time resting adults from artificially dug pit shelters, distributed centrifugally at different distances from the village were sampled. Breeding of Anopheles fluviatilis, An. annularis and An. culicifacies was found up to a distance of 1,700 m. Immature density of An. fluviatilis and An. culicifacies showed a negative correlation with the distance, but they were not statistically significant. The maximum distance at which An. fluviatilis adult females collected was 1,500 m. A significantly negative correlation was observed between An. fluviatilis resting females and distance. An. culicifacies adults were collected in low numbers even in the nearest pit shelters. No An. annularis was recorded from the pit shelters. The present record on the dispersal range of An. fluviatilis is estimated to be higher than that reported elswhere in India.

Altitude↗
PubMed1991

Infection rate and vectorial capacity of malaria vectors in Jeypore hill tract.

The role of different anophelines in malaria transmission in two geoclimatic zones, viz., Jeypore and Malkangiri plateau of Koraput distt., which are endemic for malaria, was studied. Out of 10,110 specimens belonging to 9 species collected and dissected over a period of 12 months by different methods in nine study villages, natural infection (sporozoites and oocysts) was detected in An. fluviatilis in both the zones. The sporozoite and oocyst rates were 0.28% and 1.41% in Jeypore zone and 5.09% and 0.85% in Malkangiri zone, respectively. Sporozoites were also found in a single specimen of An. culicifacies in Malkangiri area. An. annularis was incriminated in an earlier study. The vectorial capacities of An. fluviatilis, An. culicifacies and An. annularis were estimated for the three plasmodial species, viz., P. falciparum, P. vivax and P. malariae in different seasons. The definitive role played by each species in transmission is discussed.

Animals↗
PubMed1991

Pattern of rice cultivation and anopheline breeding in Koraput district of Orissa state.

The potentiality of rice fields in anopheline vector breeding in Koraput district was studied in two agricultural seasons--rubi and kharif. Altogether, 17 species were recorded from the rice fields. The terraced stream bed paddy-fields with a perceptible water flow in top-hill areas support heavy breeding of the principal vector A. fluviatilis at all stages of paddy growth. A. culicifacies and A. annularis breeding became scarce when the paddy plants reached a height of 80 cm. Vector species formed 2 per cent in rabi and 32 per cent in kharif of the anopheline fauna from the paddy fields and the maximum production was during early stage of paddy growth or after harvesting.

Agriculture↗
PubMed1990

Breeding habitats of malaria vectors: A. fluviatilis, A. annularis and A. culicifacies, in Koraput district, Orissa.

Anopheline breeding habitats were studied in two different geoclimatic zones. The vectors A. fluviatilis, A annularis and A. culicifacies breed in all types of habitats. Streams were most productive for the main vector, A. fluviatilis and breeding was intense during winter and early summer. In the rainy season, breeding occurred in terraced paddy fields. A. culicifacies were produced in large numbers in rivers in summer and in paddy fields in rainy and cold seasons. Considering the vastness of these breeding habitats, vector control measures by larviciding or any other bioenvironmental means will not be a feasible alternative even though house spraying poses serious problems in this area due to several reasons. The use of personal protection methods is suggested.

Animals↗