Additional remarks phenotype | Mutant/mutation
Mutant in which the crt gene of P. berghei is replaced by the P. falciparum crt gene (MAL7P1.27) of the chloroquine (CQ) sensitive HB3-strain (with a C-terminal V5 epitope tag)
Protein (function)
The Chloroquine Resistance Transporter (CRT) is an integral membrane protein localized to the parasite's internal digestive vacuole membrane. Mutations in CRT result in a decreased accumulation of chloroquine within the digestive vacuole in the parasite as a result of increased transport of chloroquine.
Phenotype
The phenotype analyses of mutant PbHB3 indicate that CRT of P. falciparum can complement the function of CRT of P. berghei. A conserved function of CRT in different Plasmodium species is also supported by the high degree of sequence identity (~64%) between pfcrt and its orthologs in rodent Plasmodium species.
Asexual blood stages of mutant PbHB3 and wild type P. berghei showed the same (in vitro and in vivo) sensitivity to chloroquine and amodiaquine.
Evidence is presented that in the presence of chloroquine, the mutant PbHB3 is at a selective disadvantage during mosquito transmission compared to mutant RMgm-611 (Pb7G8) in which the crt gene of P. berghei is replaced by the P. falciparum crt gene of the chloroquine (CQ) resistant 7G8-strain. (Limited) evidence (based on morphology of gametocytes) is presented that in the presence of chloroquine gametocytes of PbHB3 and wild type P. berghei are affected (pigment clumping) whereas gametocytes of mutant Pb7G8 showed wild type morphology in the presence of chloroquine.
Additional information
The crt gene of the CQ resistant P. falciparum strain 7G8 carries 5 point mutations, resulting in amino acid changes C72S, K76T, A220S, N326D, and I356L. This SVMNT (codon 72–76)-type haplotype is common in South America and Papua New Guinea and is occasionally observed in Southeast Asia and India.
See mutant RMgm-611 (Pb7G8) in which the crt gene of P. berghei is replaced by the P. falciparum crt gene of the chloroquine (CQ) resistant 7G8-strain (with a C-terminal V5 epitope tag). The P. berghei mutants PbHB3, Pb7G8 and wild type P. berghei showed the same (in vitro and in vivo) sensitivity to chloroquine and amodiaquine.
Attempts have been made to introduce a CVIET-type pfcrt allele (common in Africa) from the CQ-resistant Dd2 strain, which encodes 8 polymorphisms (M74I, N75E, K76T, A220S, Q271E, N326S, I356T, and R371I); however, attempts failed to obtain integration of this allele into the pbcrt locus.
See RMgm-612 for unsuccessful attempts to disrupt the crt gene of P. berghei, indicating an essential role of CRT during asexual blood stage development. In earlier studies in P. falciparum, the failure to disrupt pfcrt suggested an essential role of CRT for asexual blood stage viability (Waller et al., 2003, J. Biol. Chem. 278, 33593-601).
Other mutants
RMgm-611: A mutant in which the crt gene of P. berghei is replaced by the P. falciparum crt gene of the chloroquine (CQ) resistant 7G8-strain (with a C-terminal V5 epitope tag)
RMgm-612: unsuccessful attempt to disrupt crt of P. berghei
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