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Biomedical subjects

K L Yap

Publications and source records attributed to K L Yap.

At least 19 recordsLinked to original sources
PubMed2000

Calmodulin target database.

The intracellular calcium sensor protein calmodulin (CaM) interacts with a large number of proteins to regulate their biological functions in response to calcium stimulus. This molecular recognition process is diverse in its mechanism, but can be grouped into several classes based on structural and sequence information. We have developed a web-based database (http://calcium.uhnres.utoronto.ca/ctdb) for this family of proteins containing CaM binding sites or, as we propose to call it herein, CaM recruitment signaling (CRS) motifs. At present the CRS motif found in approximately 180 protein sequences in the databases can be divided into four subclasses, each subclass representing a distinct structural mode of molecular recognition involving CaM. The database can predict a putative CRS location within a given protein sequence, identify the subclass to which it may belong, and structural and biophysical parameters such as hydrophobicity, hydrophobic moment, and propensity for alpha-helix formation.

Amino Acid Sequence↗
PubMed1999

Diversity of conformational states and changes within the EF-hand protein superfamily.

The EF-hand motif, which assumes a helix-loop-helix structure normally responsible for Ca2+ binding, is found in a large number of functionally diverse Ca2+ binding proteins collectively known as the EF-hand protein superfamily. In many superfamily members, Ca2+ binding induces a conformational change in the EF-hand motif, leading to the activation or inactivation of target proteins. In calmodulin and troponin C, this is described as a change from the closed conformational state in the absence of Ca2+ to the open conformational state in its presence. It is now clear from structures of other EF-hand proteins that this "closed-to-open" conformational transition is not the sole model for EF-hand protein structural response to Ca2+. More complex modes of conformational change are observed in EF-hand proteins that interact with a covalently attached acyl group (e.g., recoverin) and in those that dimerize (e.g., S100B, calpain). In fact, EF-hand proteins display a multitude of unique conformational states, together constituting a conformational continuum. Using a quantitative 3D approach termed vector geometry mapping (VGM), we discuss this tertiary structural diversity of EF-hand proteins and its correlation with target recognition.

Amino Acid Motifs↗
PubMed1999

Evidence for calmodulin inter-domain compaction in solution induced by W-7 binding.

Small-angle X-ray scattering and nuclear magnetic resonance were used to investigate the structural change of calcium-bound calmodulin (Ca2+/CaM) in solution upon binding to its antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7). The radius of gyration was 17.4+/-0.3 A for Ca2+/CaM-W-7 with a molar ratio of 1:5 and 20.3+/-0.7 A for Ca2+/CaM. Comparison of the radius of gyration and the pair distance distribution function of the Ca2+/CaM-W-7 complex with those of other complexes indicates that binding of two W-7 molecules induces a globular shape for Ca2+/CaM, probably caused by an inter-domain compaction. The results suggest a tendency for Ca2+/CaM to form a globular structure in solution, which is inducible by a small compound like W-7.

Animals↗
PubMed1999

Recovery of poliovirus from cut surface of stored fresh papaya fruit.

Poliovirus kept on the cut surfaces of fully ripe papaya cubes placed in an ice box showed a sharp and significant reduction in the recovery of infectious virus about 15 minutes after exposure. Thereafter, a very gradual decrease ensued and infectious residual virus was detected up to the end of the 6-hour exposure period. Papaya cubes washed or kept overnight before virus inoculation, and from less ripe fruits produced a similar survival pattern. A very small proportion of the inoculum was recovered from the mashed content of the inoculated papaya cubes thus suggesting that most of the non-recovered virus particles were inactivated. The results suggest that the importance of poliovirus-contaminated cut papayas as a transmission vehicle for the virus is greatly reduced by the rapid decline in the infectivity of a large proportion of the virus soon after contamination. Nevertheless, the potential to transmit remains as a small residual pool of infectious poliovirus is able to survive for a relatively long period.

Cells, Cultured↗
PubMed1998

Rotavirus electropherotypes from the Kuala Lumpur Hospital: a re-examination after an interval of seven years.

The objective of this study was to ascertain the extent changes have occurred in the epidemiology of human rotavirus electropherotypes from the same location 7 to 8 years after an earlier study. Genomic RNA profiles of rotaviruses from diarrhoeic children admitted to the Kuala Lumpur Hospital from April to December 1996 were determined by polyacrylamide gel electrophoresis and silver staining. A total of 179 group A rotaviruses were detected from 870 children: 175 with legible staining of all RNA segments were classified into 14 distinct electropherotypes (10 and 4 with long and short migration patterns respectively). In addition, the results revealed: high predominance of long pattern electropherotypes (94% of the total electropherotypes); most long electropherotypes with RNA profiles which all 11 RNAs migrated separately (8 of 10 electropherotypes); all short electropherotypes had segments 2 and 3 that co-migrated; presence of a very numerically dominant electropherotype (75% of all electropherotypes); frequent co-circulation of the dominant electropherotype-present throughout the study period--with other electropherotypes present for limited periods; sequential temporal appearances by similar electropherotypes. These observations were similar to that of an earlier study conducted in 1988/89. Nevertheless, the dominant electropherotype in the present study was different and not among the electropherotypes detected in the earlier study.

Diarrhea, Infantile↗
PubMed1997

Mechanical transport of rotavirus by the legs and wings of Musca domestica (Diptera: Muscidae).

Factors affecting the mechanical transmission of rotavirus by the legs and wings of the housefly, Musca domestica L., were examined in a laboratory study. Rotavirus was picked up when houseflies walked on thin smears of clarified rotavirus suspensions. The addition of glycerol, which increased viscosity of the virus suspension, and particulate human feces slightly increased the proportion of flies contaminated with virus. However, the addition of glycerol greatly reduced the average number of virus particles picked up per fly, whereas feces greatly increased the number of particles. The proportion of flies with virus-contaminated legs, which transferred virus to > 1 contact surface, was increased by longer contact time with the surface and when the contact surface was agar instead of glass. Most virus particles were deposited on 1st contact with the surface. Most flies dislodged virus particles inoculated on the underside of their wings soon after the start of simulated flight. Our data indicated that the nature of the virus-suspending medium has a greater effect on the level of virus contamination than on the ability to become contaminated. The importance of walking as a mode of virus transport depends on the nature of the contact surface, the risk of the contaminated fly settling first on a surface likely to come into contact with humans, and fly numbers.

Animals↗
PubMed1997

Detection of false positives by incorporation of a confirmatory blocking test into a commercial enzyme-linked immunosorbent assay specific for adenovirus antigen.

A blocking test was incorporated into the commercial IDEIA Adenovirus test (DAKO Diagnostics Ltd., Cambridgeshire, UK) to detect false positive results when faecal specimens were tested for adenovirus antigen. Immune rabbit serum raised against pooled adenovirus particles from human faecal specimens, together with the pre-immune serum, was used. Assessment of positive showed that false positives were produced under two different conditions: when results were based on visual determination instead of a cut-off value determined from photometric reading, and when absorbance values were not immediately read at the end of the test. Under the optimum condition for reading and assessment of test results (immediate reading and photometric determination), 11% of 65 adenovirus-positive samples were checked by the blocking ELISA as false positives. The rest of the specimens showed blocking of positive absorbance values by 70 to 98%. ELISA was found to be more sensitive than immune electron microscopy on samples with lower antigen concentration.

Adenovirus Infections, Human↗
PubMed1994

Infectivity titration of the fast-replicating and cytopathic hepatitis A virus strain HM175A.2 by an in situ enzyme immunoassay.

A simple, rapid and objective infectivity assay based on an in situ enzyme immunoassay (EIA) was developed for the fast-growing and cytopathic cell culture-adapted hepatitis A virus (HAV) strain HM175A.2. Infectivity titration by EIA correlated well with titration by cytopathic effects. The reliability of this assay was demonstrated by close agreement in virus infectivity titers among different assays of the same virus aliquot and between assays of different virus aliquots. HAV infected cell cultures after fixation could be stored for up to 1 week before testing without decline in virus titer.

Antigens, Viral↗
PubMed1993

Invasive aspergillosis--a rabbit model.

An invasive aspergillosis model in rabbits was attempted using 3 concentrations of A. fumigatus conidia. Conidia concentrations of 1 x 10(6), 1 x 10(7) and 1 x 10(8) were inoculated intravenously into rabbits. The severity of infection was directly proportional to the inoculum size of the conidia. Aspergillus fumigatus was isolated from livers, kidneys, spleens, hearts and lungs of infected rabbits at a rate of 82%, 75%, 57%, 54% and 32% respectively. Cultures of urine specimens taken by bladder tap were positive for A. fumigatus in 30% of the rabbits tested. Blood cultures using the Bactec Fungal System (Becton Dickinson Corp., USA) failed to isolate A. fumigatus in 20 rabbits with biopsy-proven invasive apergillosis. Active infection with high fungal tissue burden occurred between 2-4 days after infection in rabbits inoculated with 1 x 10(7) conidia.

Animals↗
PubMed1992

Rotavirus electropherotypes in Malaysian children.

A 12-month study was carried out on the molecular epidemiology of rotavirus in urban and suburban Malaysian children. Analysis of faecal samples from 973 hospitalized diarrhoeic children by polyacrylamide gel electrophoresis detected 268 rotaviruses (28%). All isolates were group A rotaviruses, which produced 22 electropherotypes: 16 (91.5%) with long RNA migration patterns and 6 (8.5%) with short patterns. One of the long-pattern electropherotypes was the predominant strain (71.1% of the total electropherotypes) isolated during this study. Although 3 other strains were detected sporadically over the study period, 16 others were present only during the first 7 months and 2 others were confined to the last 5 months. Long- and short-pattern electropherotypes were found to co-circulate extensively. There was a significant association of short-pattern electropherotypes with infection in older children. In addition, the prevalence of vomiting and mean duration of diarrhoea were significantly associated with different electropherotypes.

Child↗
PubMed1992

A one year community-based study on the incidence of diarrhoea and rotavirus infection in urban and suburban Malaysian children.

A 1 year longitudinal study of 156 Malaysian children from urban and suburban areas in the Klang Valley revealed that the incidence rate of diarrhoea was 23.6 per 100 person-year with abnormal faeces reported on 0.26% of the total days of observation. Diarrhoea cases were detected in children from all socioeconomic classes. Rotavirus was isolated from 12% of the diarrheic children and asymptomatic rotavirus infection occurred in 3.2% of the children. All rotaviruses isolated were group A rotaviruses with long electrophoretypic pattern.

Child, Preschool↗
PubMed1992

An evaluation of the staphylococcal co-agglutination test for the detection of group A rotavirus in human faeces.

The group A rotavirus staphylococcal co-agglutination test was evaluated and its sensitivity and specificity compared with an in-house enzyme-linked immunosorbent assay (ELISA) and a commercial latex agglutination test (Rotalex). In addition, the storage stability of the staphylococcal reagents was ascertained. Examination of 136 clarified suspensions of diarrhoeal faeces by the staphylococcal co-agglutination test revealed a high proportion of false positives (26%) and uninterpretable results (34%) due to non-specific agglutination. Non-specific agglutination could be removed effectively by prior absorption of the clarified faecal specimens with unsensitized staphylococci. The staphylococcal co-agglutination test was less sensitive and specific than the in-house enzyme-linked immunosorbent assay but was comparable to the Rotalex slide latex agglutination test. The staphylococcal reagents have a shelf life of at least 29 weeks.

Agglutination Tests↗
PubMed1984

Induction and Ly phenotype of suppressor T cells in mice during primary infection with dengue virus.

Infection of mice with dengue-4 virus produced a significant, transient immunosuppression of the delayed-type hypersensitivity (DTH) response to sheep red blood cells (SRBC). Suppression was noted on day 3 after infection, was maximal on day 5 and was no longer evident on day 13 after infection. The suppressive effect was transferable to normal mice by viable spleen cells from immune mice but not by immune serum. These cells appeared to be present in the spleens of infected mice as early as day 1 after infection and were still detectable on day 7. No evidence was obtained that suppression was mediated by a soluble factor. Further characterization of the cells which could transfer suppression showed them to be T cells possessing both Ly-1 and Ly-2 surface antigens. These data suggest that there may exist two types of T suppressor cells or that, alternatively, an interaction between Ly-1+ and Ly-2+ cells was required to produce suppression. The significance and implications of these findings are discussed.

Animals↗
PubMed1983

Delayed-type hypersensitivity (DTH) response to dengue virus in mice: effect of route of sensitization and splenectomy.

This study was designed to determine the role of the sensitization route and the spleen in the development of delayed-type hypersensitivity (DTH) to dengue virus in mice. DTH was measured by footpad swelling response. Strong but transient DTH was produced in cyclophosphamide (CY) pretreated mice sensitized subcutaneously (s.c.) or intravenously (i.v.) with dengue virus type 4. Subcutaneous inoculation of virus in incomplete Freund's adjuvant (IFA) further enhanced the DTH elicited. The time course of DTH generated by s.c. and i.v. sensitization were similar with the peak reactivity seen on day 6 after sensitization. Poor DTH was observed in mice given an i.p. inoculation even when CY and/or IFA were used. Intracerebral (i.c.) inoculation also sensitized mice poorly. Splenectomized mice showed enhanced DTH response when compared to intact mice. In contrast to intact mice, pretreatment of splenectomized mice with CY did not alter the DTH level. Splenectomized mice inoculated s.c. with virus in IFA showed poorer DTH than mice sensitized with virus alone.

Animals↗