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Biomedical subjects

J A Chappel

Publications and source records attributed to J A Chappel.

7 recordsLinked to original sources
PubMed1998

Modulation of antibody display on M13 filamentous phage.

Here we describe a phage vector for the display of single chain antibodies and polypeptides on the surface of filamentous M13 phage which permits facile manipulation of the valency of display. The gene encoding the polypeptide is fused to a synthetic copy of the major coat protein VIII gene (gpVIII) which permits incorporation into the phage during assembly of the filament. Here we examine the growth parameters of phage propagation on the subsequent selection of an anti-progesterone antibody fragment from a mixture of display phage. Our results suggest that the density of the polypeptides displayed on phage may be modulated by altering growth conditions. This ability to influence polypeptide display density on filamentous phage may provide a versatile approach for accessing complex libraries and the capture of weaker ligand receptor interactions by avidity, whilst the potential to access and discriminate between higher affinity interactions is not negated.

Animals↗
PubMed1995

Serum antibodies from malaria-exposed people recognize conserved epitopes formed by the two epidermal growth factor motifs of MSP1(19), the carboxy-terminal fragment of the major merozoite surface protein of Plasmodium falciparum.

The major merozoite surface protein of Plasmodium falciparum (PfMSP1) is a candidate antigen for a malaria vaccine. A 19-kDa C-terminal processing product of PfMSP1 (PfMSP1(19)) is composed of two domains sharing a cysteine-rich motif with epidermal growth factor (EGF) and is the target of monoclonal antibodies which block erythrocyte invasion in vitro. We have evaluated human antibody responses to PfMSP1(19) by using recombinant proteins representing the EGF motifs encoded by the two main alleles of the MSP1 gene. We find that both EGF motifs are antigenic but that only 10 to 20% of malaria-exposed individuals have serum antibodies that recognized either of the motifs. When both EGF motifs were expressed together as a single protein, they were recognized by more than 40% of sera from malaria-exposed individuals. Major epitopes recognized by human antibodies are dependent upon the correct tertiary structure of the protein and are cross-reactive between the different allelic sequences of PfMSP1(19). This suggests that antibodies induced by vaccination with one or the other allelic forms of the protein could recognize all strains of P. falciparum. Immunoglobulin G (IgG) subclass-specific enzyme immunoassays indicate that PfMSP1(19) antibodies are predominantly of the IgG1 subclass.

Adolescent↗
PubMed1994

Naturally acquired human antibodies which recognize the first epidermal growth factor-like module in the Plasmodium falciparum merozoite surface protein 1 do not inhibit parasite growth in vitro.

Merozoite surface protein 1, one of the major surface proteins of the invasive blood stage of the malaria parasite, is a prime candidate for the development of a vaccine against the human disease. Previously, monoclonal antibodies which both inhibited the growth of Plasmodium falciparum in vitro and bound to the first of two epidermal growth factor-like modules located near the carboxy terminus of the protein had been identified. In this study, we have used affinity chromatography on a recombinant fusion protein corresponding to the first epidermal growth factor-like module in P. falciparum merozoite surface protein 1 to prepare antibody induced by natural infection. The antibody was purified from the total immunoglobulin G fraction of adult West African donors, shown to passively confer immunity against falciparum malaria. Such affinity-purified antibodies were shown to recognize the native protein by a number of separate criteria and to block the binding of an inhibitory monoclonal antibody, but they failed to inhibit parasite invasion in an in vitro growth assay. These results indicate that antibody alone is not sufficient to interfere with erythrocyte invasion.

Adult↗
PubMed1993

Monoclonal antibodies that inhibit Plasmodium falciparum invasion in vitro recognise the first growth factor-like domain of merozoite surface protein-1.

A major protein found on the surface of the invasive stage of the malaria parasite Plasmodium falciparum, merozoite surface protein-1 (MSP1), has been proposed as a vaccine candidate. Antibodies which recognise a single fragment of this molecule (MSP1(19)), composed of 2 regions related to epidermal growth factor (EGF), also inhibit parasite growth in vitro. It is shown by direct expression of the individual EGF-like domains in Escherichia coli, that the first domain is the target of growth-inhibitory antibodies. A single amino acid difference influences the binding of some antibodies to this domain.

Amino Acid Sequence↗
PubMed1993

A conserved parasite serine protease processes the Plasmodium falciparum merozoite surface protein-1.

The merozoite surface protein-1 of the human malaria parasite Plasmodium falciparum undergoes an extracellular proteolytic cleavage (secondary processing) intrinsic to successful erythrocyte invasion. In the T9/96 clone of P. falciparum the protease responsible has been characterised as a membrane-associated, calcium-dependent activity, sensitive to irreversible inhibitors of serine proteases. Here we extend these studies and show that secondary processing activity in intact merozoites of P. falciparum strains expressing the alternative dimorphic type of merozoite surface protein-1 has identical characteristics, and that the cleavage site is close to or identical to that in the protein from T9/96. The protease responsible is shown to be parasite-derived, and able to catalyse processing of native substrate only when present in the same membrane. Cleavage of the substrate follows apparent first order kinetics for at least 2 half-lives. It is concluded that secondary processing of both dimorphic forms of the P. falciparum merozoite surface protein-1 is a conserved event, mediated by a mechanistically conserved protease located on the merozoite surface. These observations provide clues to the identity of the protease and show that, irrespective of the dimorphic type, secondary processing results in the same, highly conserved region of the merozoite surface protein-1 remaining on the surface of the invading merozoite.

Animals↗
PubMed1992

A malaria merozoite surface protein (MSP1)-structure, processing and function.

Merozoite surface protein-1 (MSP-1, also referred to as P195, PMMSA or MSA 1) is one of the most studied of all malaria proteins. The protein is found in all malaria species investigated and structural studies on the gene indicate that parts of the molecule are well-conserved. Studies on Plasmodium falciparum have shown that the protein is in a processed form on the merozoite surface, a result of proteolytic cleavage of the large precursor molecule. Recent studies have identified some of these cleavage sites. During invasion of the new red cell most of the MSP1 molecule is shed from the parasite surface except for a small C-terminal fragment which can be detected in ring stages. Analysis of the structure of this fragment suggests that it contains two growth factor-like domains that may have a functional role.

Amino Acid Sequence↗