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The complete sequence of the gene for the knob-associated histidine-rich protein from Plasmodium falciparum
Abstract:
'Knobs' at the surface of erythrocytes infected with mature stages of Plasmodium falciparum are believed to be important in adherence of these cells to capillary walls. They contain at least one parasite protein, designated the knob-associated histidine-rich protein (KAHRP). We present here the sequences of a cDNA and chromosomal clone that predict the complete sequence of KAHRP. The gene contains a single intervening sequence, located at the 3' boundary of the hydrophobic core of a putative signal sequence. Exon two encodes a short region that is rich in histidine as well as two separate regions of repetitive sequence, the 5' repeats (five copies related to SKKHKDNEDAESVK) and the 3' repeats (seven copies related to SKGATKEAST). These repeat blocks were both shown to bear epitopes recognized by the human immune system during natural infection by expressing them separately in Escherichia coli, and reacting human antibodies affinity-purified on lysates of the resulting clones with the corresponding synthetic oligopeptides. The 3' end of the molecule, presumably the repetitive region, is a site of size variation in KAHRP from different isolates.
Insights
Knob-associated histidine-rich protein (KAHRP) sequences were determined for Plasmodium falciparum. Repeat regions within KAHRP are recognized by the human immune system during infection.
Area of Science:
- Malariology
- Molecular Parasitology
- Immunology
Background:
- Adherence of Plasmodium falciparum-infected erythrocytes to capillaries is mediated by 'knobs'.
- Knobs contain knob-associated histidine-rich protein (KAHRP), a key parasite protein.
- Understanding KAHRP structure and function is crucial for malaria pathogenesis research.
Purpose of the Study:
- To determine the complete sequence of KAHRP.
- To investigate the immunogenic properties of KAHRP repeat regions.
- To explore the basis of KAHRP size variation.
Main Methods:
- cDNA and chromosomal cloning to obtain KAHRP gene sequences.
- Expression of KAHRP repeat regions in Escherichia coli.
- Affinity purification of human antibodies and reaction with synthetic oligopeptides.
Main Results:
- The complete KAHRP sequence was predicted from cDNA and chromosomal clones.
- Exon two contains histidine-rich regions and two distinct repeat blocks (5' and 3').
- Both repeat blocks contain epitopes recognized by human antibodies during natural infection; the 3' end shows size variation.
Conclusions:
- The KAHRP gene structure and sequence have been elucidated.
- Specific repeat regions of KAHRP are immunogenic and recognized by the human immune system.
- The repetitive 3' region of KAHRP exhibits size variation across different parasite isolates.