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Malaria caused by an infection of Plasmodium knowlesi can result in high parasitemia and deaths. Therefore, effective and prompt treatment is necessary to reduce morbidity and mortality. The study aims to characterize P. knowlesi dihydrofolate reductase-thymidylate synthase enzyme (PkDHFR-TS) and its sensitivity to antifolates. The putative Pkdhfr gene was PCR amplified from field isolates collected from the Southern Thailand. Molecular analysis showed 11 polymorphisms in the dhfr domain of the bifunctional dhfr-ts gene. Of these, 1 polymorphism was a non-synonymous substitution (R34L) that had previously been reported but not associated with antifolate resistance. The recombinant PkDHFR-TS enzyme was found to be sensitive to standard antifolates-pyrimethamine and cycloguanil-as well as P218, a registered candidate drug currently first in human clinical trial. Results suggest that antifolates class of compounds should be effective against P. knowlesi infection., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The various stages of the malaria parasites in the vertebrate host and in the mosquito vector offer numerous candidates for vaccine and drug development. However, the biological complexity of the parasites and the interaction with the immune system of the host continue to frustrate all such efforts thus far. While most of the targets for drug and vaccine design have focused on the asexual stages, the sexual stages of the parasite are critical for transmission and maintenance of parasites among susceptible vertebrate hosts. Sexual stage parasites undergo a series of morphological and biochemical changes during their development, accompanied by a co-ordinated cascade of a distinct expression pattern of sexual stage specific proteins. Mechanisms underlying the developmental switch from asexual parasite to sexual parasite still remain elusive. Methods that can break the malaria transmission cycle thus occupy a central place in the overall malaria control strategies. This paper provides a review of genes expressed in sexually differentiated Plasmodium. In the past few years, a molecular approach based on targeted gene disruption has revealed fascinating biological roles for many of the sexual stage gene products. In addition, we will briefly discuss other functional genomic approaches employed to study not only sexual but also other aspects of host-parasite biology.

The differentiation and development of sexual stages in Plasmodium falciparum is a complex process which involves the expression of several sexual stage-specific proteins. Pfg27 is one of the most crucial proteins and is expressed abundantly at the onset of gametocytogenesis. An expression and purification system for Pfg27 has been established that yields approximately 5 mg l(-1) of purified protein in a soluble form. This protein has been crystallized by the hanging-drop vapour-diffusion method using PEG 8000 as a precipitant. The original crystal size was improved significantly by the addition of glucose to the reservoir solution. Pfg27 crystals belong to the space group C222(1), with unit-cell parameters a = 58.9, b = 113.2, c = 91.6 A. Native diffraction data were collected under cryogenic conditions and phase resolution by a selenomethionine-aided multiple-wavelength anomalous dispersion technique is in progress. The Pfg27 structure will provide a framework for functional and biochemical studies aimed at understanding gametocyte development in P. falciparum.