Molecular cloning and expression in Escherichia coli of a malaria exoantigen from Plasmodium falciparum, putative candidate for vaccine
Zhou, Ping
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Permalink
https://hdl.handle.net/2142/20254
Description
Title
Molecular cloning and expression in Escherichia coli of a malaria exoantigen from Plasmodium falciparum, putative candidate for vaccine
Author(s)
Zhou, Ping
Issue Date
1991
Doctoral Committee Chair(s)
Hager, Lowell P.
Department of Study
Biochemistry
Discipline
Biochemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Molecular
Chemistry, Biochemistry
Language
eng
Abstract
Malaria remains as one of the biggest public health problems in the world today. Plasmodium falciparum is the most lethal among the four species of protozoa that cause malaria infection in humans. In the parasite life cycle the asexual blood stage is responsible for the clinical manifestations of the disease, thus the studies of the immune response and the development of vaccine for this stage are critical to decreasing the morbidity and mortality of malaria.
"In the blood stage, the parasite releases ""exoantigens"" into the host blood stream or secretes them into the culture supernatant of in vitro parasite cultures. These exoantigens are believed to either be shed or secreted from the parasite during red blood cell invasion. Previous experiments using partially purified exoantigen from in vitro cultures showed that these exoantigens could protect experimental monkeys from infection. In addition, recent studies have shown that the exoantigens could trigger tumor necrosis factor (TNF) secretion from macrophages. The elevated TNF level is responsible for the pathological consequences of malaria in humans and animals. A vaccine based on these exoantigens could potentially disrupt the malaria blood cycle and block the triggering of TNF secretion."
This research focuses on the blood stage exoantigens. The goal of this study was to clone and express one of the exoantigens so that the potential vaccine valve of exoantigen could be assessed by immunological studies.
A cDNA clone of 2.5 Kb coding for a portion of new exoantigen was identified through the combined screening with human immune IgG and anti-SP antibody. The cloned cDNA is 2.5 Kb in size with 1827 base pairs of coding region for a polypeptide of 70 Kd having 608 amino acid residues. The polypeptide has two blocks of repeating sequences, a characteristic of malaria proteins. The polypeptide is very acidic and consequently is negatively charged due to the presence of many glutamic acid residues. No hydrophobic stretch amino acids which could represent a membrane anchoring sequence is present in the protein sequence. Thus, this protein is considered to be a new soluble exoantigen. There is no 5$\sp\prime$ end starting codon in this clone, therefore, it codes for only a portion of a large exoantigen. The DNA and amino acid sequences of the gene were checked through the BIONET data base, and no homolog to any published malaria or human sequences was found. Therefore, we have cloned a new exoantigen from the malaria parasite Plasmodium falciparum.
The 70 Kd polypeptide was produced in a fusion form and purified with an affinity column. This purified exoantigen could be used for further immunological studies to evaluate its vaccine potential.
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