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Y D Sharma

Publications and source records attributed to Y D Sharma.

At least 37 records · Page 2Linked to original sources
PubMed1996

Allelic forms of the knob associated histidine-rich protein gene of Plasmodium falciparum.

The knob associated histidine-rich protein (KAHRP) gene was cloned and sequenced from two Indian isolates of Plasmodium falciparum, Pf3-92 and Pf29-92. These isolates showed major sequence differences in the C-terminal repeat domain of KAHRP. However, the biologically important domains such as spectrin-actin binding region remained highly conserved. The PCR amplification of a variable C-terminal repeat domain from the clinical isolates of P. falciparum, from Rajasthan epidemic, showed the presence of multiple alleles of KAHRP gene. The presence of multiple alleles indicates the existence of several P. falciparum strains in India. This should be taken into account for future malaria control strategies such as molecular therapy and vaccines.

Alleles↗
PubMed1995

Malaria menace.

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Animals↗
PubMed1994

Enhanced expression of Plasmodium falciparum heat shock protein PFHSP70-I at higher temperatures and parasite survival.

The effect of various body temperatures, encountered during malaria fever, on the synthesis of Plasmodium falciparum heat-shock protein called PFHSP70-I and parasite growth rates among five different isolates are described. The results show that after the exposure of parasites at 39 degrees C for 30 min the amount of PFHSP70-I in all five isolates increased markedly and significantly, whereas parasite growth rates and the amount of total blood stage antigens remained almost unaffected. This indicates that the PFHSP70-I gene responds to heat-shock by producing higher amounts of PFHSP70-I protein, presumably to protect the parasite from being killed during malaria fever.

Animals↗
PubMed1994

Plasmodium vivax: immune responses in a cross-section of the population in the Delhi area of India.

The immune status of the individuals living in the Delhi area of northern India where Plasmodium vivax is predominant is described. The majority of the individuals who were acutely infected with P. vivax had antibodies against crude blood-stage antigen and the recombinant antigen, PV9. In contrast, the peripheral blood mononuclear cells of the majority of these individuals did not show proliferation in the presence of either of these antigens. There was no correlation between antibody levels and T cell proliferation. Such an immune status of individuals living in endemic areas should be taken into account in the future in developing P. vivax malaria vaccines.

Adolescent↗
PubMed1992

Effect of heat-shock on Plasmodium falciparum viability, growth and expression of the heat-shock protein 'PFHSP70-I' gene.

Cultures of the human malaria parasite Plasmodium falciparum were subjected to heat-shock for varying times and temperatures and then tested for their viability, growth and expression of heat-shock protein. Results show that the majority of parasites remained viable after heat-shock but their growth was affected. However, the expression of the heat-shock protein 'PFHSP70-I' gene was enhanced after heat-shock. We conclude that malarial parasites are able to survive in vivo during fever probably due to the overexpression of the heat-shock protein gene.

Animals↗
PubMed1992

Cloning and developmental expression of the alpha 3 chain of chicken type IX collagen.

Fibrous and nonfibrous collagens comprise two major groups within the collagen family and both groups are found in a diverse variety of tissue fabrics. Type IX collagen is in the nonfibrous group; three different subunits of type IX collagen have been identified and the alpha 1 and alpha 2 subunits have been cloned. Using molecular cloning methods we have isolated, from an embryonic chicken cartilage library, cDNA clones which code for the entire alpha 3 chain of chicken type IX collagen. The cDNA clones encompass 2416 base pairs which have a conceptual open reading frame for a protein containing 675 amino acids including 193 Gly-X-Y repeats. These collagen repeats are in three separate domains which are interspersed with four major noncollagen domains. The collagen repeats also have four minor interruptions. This chain organization directly aligns with both the alpha 1 and alpha 2 chains of chicken type IX collagen. Comparison of the deduced amino acid sequence with peptide sequences of type IX collagens shows identity with 95 of the 96 known residues of the chicken alpha 3 chain and 81 of the 98 known residues of the bovine alpha 3 chain. The identical residues match those in five peptide fragments, two from the bovine protein and three from the chicken protein. The chicken and bovine alpha 3 chains have conserved cross-linking sites, separated by 137 residues which span 40 nm, the length of the hole zone in a collagen fibril. The NC3 domain of the chicken alpha 3 chain contains a repeat Cys-Pro motif which is present in both vertebrate and invertebrate nonfibrillar collagens. Northern blot hybridization exhibits a major mRNA of about 3.3 kilobases; this transcript is found in cartilaginous tissues in the embryo, including the developing limb and is not detected in other tissues or in the precondensation stage of limb development. The composite data delineate the primary structure of the alpha 3 chain of chicken type IX collagen, show its close relationship to the alpha 1 and alpha 2 chains, demonstrate its mRNA transcript, and show the appearance of that transcript in tissues of the developing chick embryo.

Amino Acid Sequence↗
PubMed1992

Molecular cloning and serological characterization of a new Plasmodium vivax recombinant antigen which contains apolipoprotein B-100 like sequences.

We have isolated a new recombinant antigen 'PV12' of Plasmodium vivax by immunological screening of the genomic library. The antigen shows a sequence homology with human apolipoprotein B-100. A large number of P. vivax infected individuals (79%) were seropositive against this antigen. The probable function of this antigen could be to evade the host defence system (i) by inactivating the perforin of natural killer cells and (ii) by engaging the host immune system to produce antibodies against this decoy antigen.

Amino Acid Sequence↗
PubMed1992

Structure and possible function of heat-shock proteins in Falciparum malaria.

Like many prokaryotes and eukaryotes, the malaria parasite also synthesizes several stress proteins. Most widely studied stress proteins of this parasite are the heat-shock proteins (hsps). Their discovery in malaria is a gift of recombinant DNA technology. Five hsp genes from Plasmodium falciparum have been identified which are located on different chromosomes. Thus the inheritance and expression of hsp genes are independent of each other. They share a large amount of sequence homology at N-terminus with the hsps of other organisms. Their gene regulatory sequences and other elements, important for gene expression, are yet to be determined. The biological role of these proteins in malaria is not fully understood but it is possible that they provide protection to the parasite from various stresses encountered in the host. In this process hsps probably bind to the toxic molecules as well as damaged proteins to flush them out of the parasite. Their involvement in the stage-specific parasite transformation to increase the infectivity and virulence, as observed in other parasites, remains to be determined. Malarial hsps are antigenic in humans. This antigenicity could be attributed to the non-homologous sequences in the C-terminus region. The potential of one of them (pfhsp 70I) for a future malaria vaccine and immunodiagnostics requires re-evaluation of the data.

Amino Acid Sequence↗
PubMed1991

Recombinant fusion protein identified by lepromatous sera mimics native Mycobacterium leprae in T-cell responses across the leprosy spectrum.

Pooled polyvalent sera from lepromatous leprosy patients were used to screen a lambda gt11 recombinant DNA expression library of Mycobacterium leprae in order to identify the relevant antigens recognized by the human immune response. Of the 300,000 phages screened, 4 clones were identified that coded for fusion proteins of the same molecular mass. The fusion protein from clone LSR2 was tested for immunoreactivity in assays using peripheral blood cells and sera from 11 laboratory personnel and 105 patients across the leprosy spectrum. LSR2 protein appears to be predominantly a T-cell antigen. It evokes similar lymphoproliferative responses as the native bacillus both at the individual level and in the leprosy spectrum as a whole. Though only 50% of patient sera with anti-M. leprae antibodies reacted with the fusion protein, the pattern of reactivity in the antibody responses was also similar for the various clinical types. The coding regions of clones LSR1 and LSR2 are identical. They show no homology with sequences stored in data banks and encode a protein of 89 amino acids with a calculated molecular mass of approximately 10 kDa.

Amino Acid Sequence↗
PubMed1991

Knobs, knob proteins and cytoadherence in falciparum malaria.

1. The sequestration of trophozoite and schizont infected erythrocytes (IRBC) in post-capillary venules of host internal organs causes most of the morbidity and mortality in falciparum malaria. It is a knob mediated cytoadherence phenomenon where knobs act as the focal junction between IRBC and host endothelial cell. Knobless (K-) parasites, isolated from cultures (not yet isolated from in vivo), do not cause virulent infections. Knobs thus play an important role in pathophysiology of falciparum malaria. 2. The chemical composition of knobs is partly explored, several proteins (Known as knob proteins) have been identified. According to their function they can be classified as (a) knob-inducing protein, "KAHRP" (b) knob-associated cytoadherent proteins, e.g. PFEMP-1, modified band 3 and an antigen recognized by monoclonal 33G2 and (c) knob-associated structural protein, e.g. PFEMP-2/MESA/PP-300. Most of them show size polymorphism among different isolates. Only KAHRP and MESA/PFEMP-2 have been studied at molecular level. Their chromosomal locations have been identified such as KAHRP on chromosome 2 and MESA/PFEMP-2 on chromosomes 5 and 6. 3. The receptor molecules on endothelial cells for knob ligands have been identified and partially characterized. 4. Knob ligands and their receptor molecules can play an important role in developing the immunotherapeutic reagents. 5. Based on the available data a tentative hypothesis has been proposed about the loss of knobs in vitro. Nevertheless, this needs further support from other experimental evidence. 6. Future work should be directed towards the structure and function of knob proteins and their interactions with each other as well as with host proteins. Regulation of expression of knobs and knob protein(s), evaluation of knob antigens for immunotherapy of severe falciparum malaria and for a malaria vaccine also require further investigations.

Amino Acid Sequence↗
PubMed1991

Lack of correlation between red cell invasion by merozoites and anti-heat shock protein-70 antibody levels in malaria patients' sera.

A total of 172 sera samples were collected from individuals who were living in Piyawli-Jaitwarpur village in Ghaziabad district (U.P.), India. They had suffered from falciparum malaria attack, and were cured with antimalarial drugs 1-2 weeks prior to sample collection. These samples were divided into nine groups according to their age. The pooled sera from each group were tested for the presence of anti-schizont and anti-heat shock protein (hsp)-70 antibodies, as well as for parasite growth inhibition in vitro. All sera samples showed significant levels of antibodies against schizont antigens and these levels increased with age. The sera also contained anti-hsp-70 antibodies but at lower levels and did not follow the same age-related pattern as seen with schizont antibodies. The sera from each group significantly inhibited merozoite invasion in vitro. However the same was not true for other blood stage parasites; the 2-15 years age group sera did not show significant growth inhibition of rings, trophozoites and schizonts. No correlation was observed between anti-hsp-70 antibody levels and inhibition of merozoite invasion. It is therefore concluded that the antibodies preventing the merozoite invasion could be other than anti-hsp-70 antibodies. The candidature of hsp-70 for P. falciparum malaria vaccine thus needs to be re-evaluated.

Adolescent↗
PubMed1991

Human response to a malaria vaccine candidate antigen.

The Plasmodium falciparum heat-shock protein 70 (PFHSP70) has been proposed as a potential candidate antigen for a malaria vaccine. In this study the human immune response to this antigen has been evaluated. Enzyme-linked immunosorbent assays (ELISA) were performed on serum samples collected from individuals during and after malarial infection. Only 70% of falciparum malaria patients responded to this antigen during the natural course of infection and 54% of the recovered cases who had no parasitaemia at the time of blood collection lacked detectable antibody. The non-responders to PFHSP70 exhibited an antibody response to total schizont antigens. There was no correlation between the response against total schizont antigens and PFHSP70 antigen. The non-responsiveness against PFHSP70 was not related to age, sex or regional variations. These qualities are undesirable for a vaccine candidate antigen.

Adolescent↗
PubMed1991

Malaria and Leishmania parasites share the knob-associated histidine-rich protein gene sequences.

1. The main coding region of the knob-associated histidine-rich protein (KAHRP) gene of Plasmodium falciparum hydridized with genomic DNA of Leishmania donovani. 2. A total of five EcoRI fragments of various sizes (7.5, 5.5, 3.2, 0.75 and 0.56 Kb) were recognized by this probe, under lower stringent conditions. However, under a higher stringency of washing, two of the smallest fragments were washed away. 3. Out of these EcoRI fragments, the 5.5 Kb band showed a maximum homology with the probe which contains the histidine-rich coding sequences, whereas the 3.2 Kb band showed none. Thus there is a possibility that the Leishmania parasite also contains a KAHRP-like gene.

Animals↗
PubMed1991

Isolation and serological characterization of a Plasmodium vivax recombinant antigen.

A genomic library for Plasmodium vivax was constructed in lambda gt11 and immunologically screened with pooled serum samples from vivax patients. Six seroreactive clones were isolated, and one clone, denoted PV9, was studied further. This clone has an unusual base composition (65% G + C), does not share any homology with P. falciparum, and codes for an entirely new antigenic determinant. Antibodies (immunoglobulin G type) against the PV9-encoded polypeptide were produced in all vivax patients older than 15 years. This seroreactivity was lower among patients younger than 15 years (53%). The antigenic epitope(s) of the PV9-encoded polypeptide was recognized at a similar rate by serum samples from P. vivax patients who were living 350 to 973 km apart. Fifty percent of uninfected Indian adults were also seropositive, whereas all European and American (United States) sera tested were negative, suggesting that anti-PV9 antibodies persist after infection. The seroreactivity pattern of this antigen is similar to that of the immunity developed in malaria after repeated infections.

Adolescent↗
PubMed1988

Genomic organization, structure and possible function of histidine-rich proteins of malaria parasites.

The current status of histidine-rich proteins in malaria parasites with regard to their genomic organization, protein structure and function is discussed, one of such protein present in an avian malaria parasite Plasmodium lophurae contains about 73% histidine and called as HRP (histidine-rich protein). Among human malaria parasites, in Plasmodium falciparum, only three such proteins have been described, namely knob protein also known as knob associated histidine-rich protein (KP or KAHRP), soluble histidine-alanine rich protein (soluble HARP or PfHRP II) and small histidine-alanine rich protein (SHARP) containing 8, 35 and 30% histidine contents respectively. With rapid emergence of powerful tools in molecular biology the genes of all these histidine-rich proteins have been cloned and sequenced within a short period of time. The genomic organizations of all these proteins are very much similar to each other, in each case the gene contains a signal peptide coding sequence (exon 1) followed by an intron. This intron is followed by the main coding region (exon 2) which has no further intervening sequences. In the main coding region of each gene, the histidine-rich sequences start after 25-30 amino acids from N-terminal end (75-90 nucleotides from 5' in exon 2). All the three histidine-rich proteins of P. falciparum share some homology with the HRP of P. lophurae; they all cross react with anti HRP and incorporate higher amount of exogenous histidine. The relationship between KP and HRP resides in the repeated polyhistidine sequences, (His) 6-9, from the core of the multiple tandem repeats of HRP, whereas, the peptide Ala-His-His is commonly shared by HRP and two other proteins of P. falciparum (soluble HARP and SHARP).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Structure of the knob protein (KP) gene of Plasmodium falciparum.

We have determined the nucleotide sequence of the gene encoding the knob protein (KP) of Plasmodium falciparum (FCR-3/Gambia). The gene is interrupted by an intron which contains 34 imperfect tandemly repeated ATTTT sequences. The first exon encodes 33 amino acids with a hydrophobic core typical of signal peptides. The second exon has an open translational reading frame for 597 amino acids. The deduced protein sequence indicates that KP has multiple structural domains; unlike the N-terminal histidine-rich domain which we described previously, the C-terminal half is rich in lysine residues. Consistent with the apparent association of KP with the cytoplasmic surface of the host erythrocyte membrane, the protein is highly charged and hydrophilic.

Amino Acid Sequence↗
PubMed1987

The primary structure of a Plasmodium falciparum polypeptide related to heat shock proteins.

A cDNA library constructed from ring-stage RNA isolated from Plasmodium falciparum FCR-3/Gambia was screened with immune human serum and two related positive clones were isolated. Nucleotide sequence analysis of these recombinant clones revealed an open translational reading frame for 681 amino acids with a calculated molecular weight of 74.3 kDa. The deduced amino acid sequence of the polypeptide shows extensive homology to several heat shock proteins (hsp) which have been described. Northern and Southern hybridization analysis indicates that P. falciparum has a second gene which shares common sequences with the hsp gene described in this study.

Amino Acid Sequence↗