PfPK7, an atypical MEK-related protein kinase, reflects the absence of classical three-component MAPK pathways in the human malaria parasite Plasmodium falciparum.
Two members of the mitogen-activated protein kinase (MAPK) family have been previously characterized in Plasmodium falciparum, but in vitro attempts at identifying MAP kinase kinase (MAPKK) homologues have failed. Here we report the characterization of a novel plasmodial protein kinase, PfPK7, whose top scores in blastp analysis belong to the MAPKK3/6 subgroup of MAPKKs. However, homology to MAPKKs is restricted to regions of the C-terminal lobe of the kinase domain, whereas the N-terminal region is closer to fungal protein kinase A enzymes (PKA, members of the AGC group of protein kinases). Hence, PfPK7 is a 'composite' enzyme displaying regions of similarity to more than one protein kinase family, similar to a few other plasmodial protein kinases. PfPK7 is expressed in several developmental stages of the parasite, both in the mosquito vector and in the human host. Recombinant PfPK7 displayed kinase activity towards a variety of substrates, but was unable to phosphorylate the two P. falciparum MAPK homologues in vitro, and was insensitive to PKA and MEK inhibitors. Together with the absence of a typical MAPKK activation site in its T-loop, this suggests that PfPK7 is not a MAPKK orthologue, despite the fact that this enzyme is the most 'MAPKK-like' enzyme encoded in the P. falciparum genome. This is consistent with recent observations that the plasmodial MAPKs are not true orthologues of the ERK1/2, p38 or JNK MAPKs, and strengthens the evidence that classical three-component module-dependent MAPK signalling pathways do not operate in malaria parasites, a feature that has not been described in any other eukaryote.
Dorin
Dominique
D
INSERM U609, Wellcome Centre for Molecular Parasitology, Anderson College, 56 Dumbarton Road, Glasgow G11 6NU, Scotland, UK.
Semblat
Jean-Philippe
JP
Poullet
Patrick
P
Alano
Pietro
P
Goldring
J P Dean
JP
Whittle
Christina
C
Patterson
Shelley
S
Chakrabarti
Debopam
D
Doerig
Christian
C
D000595:Amino Acid Sequence; D000818:Animals; D017124:Conserved Sequence; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005656:Fungal Proteins / Q000737:chemistry; D015870:Gene Expression; D066298:In Vitro Techniques; D020935:MAP Kinase Signaling System; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010963:Plasmodium falciparum / Q000201:enzymology* / Q000235:genetics; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity
D004791:Enzyme Inhibitors; D005656:Fungal Proteins; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins; C503375:PK7 protein, Plasmodium falciparum; D017868:Cyclic AMP-Dependent Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases