Characterization of protein kinase CK2 from Trypanosoma brucei.

CK2 is a ubiquitous but enigmatic kinase. The difficulty in assigning a role to CK2 centers on the fact that, to date, no biologically relevant modulator of its function has been identified. One common theme revolves around a constellation of known substrates involved in growth control, compatible with its concentration in the nucleus and nucleolus. We had previously described the identification of two catalytic subunits of CK2 in Trypanosoma brucei and characterized one of them. Here we report the characterization of the second catalytic subunit, CK2alpha', and the identification and characterization of the regulatory subunit CK2beta. All three subunits are primarily localized to the nucleolus in T. brucei. We also show that CK2beta interacts with the nucleolar protein NOG1, adding to the interaction map which previously linked CK2alpha to the nucleolar protein NOPP44/46, which in turn associates with the rRNA binding protein p37. CK2 activity has four distinctive features: near equal affinity for GTP and ATP, heparin sensitivity, and stimulation by polyamines and polybasic peptides. Sequence comparison shows that the parasite orthologues have mutations in residues previously mapped as important in specifying affinity for GTP and stimulation by both polyamines and polybasic peptides. Studies of the enzymatic activity of the T. brucei CK2s show that both the affinity for GTP and stimulation by polyamines have been lost and only the features of heparin inhibition and stimulation by polybasic peptides are conserved.

Species specificity in ribosome biogenesis: a nonconserved phosphoprotein is required for formation of the large ribosomal subunit in Trypanosoma brucei.

In the protozoan parasite Trypanosoma brucei, the large rRNA, which is a single 3.4- to 5-kb species in most organisms, is further processed to form six distinct RNAs, two larger than 1 kb (LSU1 and LSU2) and four smaller than 220 bp. The small rRNA SR1 separates the two large RNAs, while the remaining small RNAs are clustered at the 3' end of the precursor rRNA. One would predict that T. brucei possesses specific components to carry out these added processing events. We show here that the trypanosomatid-specific nucleolar phosphoprotein NOPP44/46 is involved in this further processing. Cells depleted of NOPP44/46 by RNA interference had a severe growth defect and demonstrated a defect in large-ribosomal-subunit biogenesis. Concurrent with this defect, a significant decrease in processing intermediates, particularly for SR1, was seen. In addition, we saw an accumulation of aberrant processing intermediates caused by cleavage within either LSU1 or LSU2. Though it is required for large-subunit biogenesis, we show that NOPP44/46 is not incorporated into the nascent particle. Thus, NOPP44/46 is an unusual protein in that it is both nonconserved and required for ribosome biogenesis.

Transcriptome profiles of host gene expression in a monkey model of human malaria.

We used human microarrays to examine gene expression in a rhesus monkey model of human Plasmodium vivax malaria (P. cynomolgi in Macaca mulatta). Whole-blood cells were collected for extraction of RNA before infection, during both the initial liver phase of infection and bloodstream infection, and during the course of 2 bloodstream relapses. Clustering analysis showed that similarities in gene expression were greater at similar stages of the protocol for the 2 different monkeys than for the same monkey at different stages of the protocol. Interestingly, a large number of genes involved in RNA processing showed distinct down-regulation during the initial liver phase of infection. When only up-regulated genes were examined, there was evidence of an increasing number of "defense response" genes as the infection evolved but not of "cytoskeleton" genes (P

Molecular cloning of Trypanosoma brucei CK2 catalytic subunits: the alpha isoform is nucleolar and phosphorylates the nucleolar protein Nopp44/46.

We have demonstrated previously that Nopp44/46, an abundant nucleolar phosphoprotein of Trypanosoma brucei, is associated with a protein kinase. In many organisms multiple nucleolar proteins are phosphorylated by the protein kinase CK2, formerly known as casein kinase II. Here we report the identification of two T. brucei genes, CK2a1and CK2a2, which encode protein kinases bearing signature motifs common to CK2 catalytic subunits. The protein specified by CK2a1, designated CK2alpha, was capable of associating with Nopp44/46 as assessed by yeast two-hybrid analysis. An epitope-tagged version of CK2alpha expressed in T. brucei colocalized with Nopp44/46, with a largely nucleolar localization. This localization contrasts with the predominantly nuclear localization of mammalian CK2. When expressed in Escherichia coli, TbCK2alpha was catalytically active and phosphorylated Nopp44/46. Together these data demonstrate that TbCK2alpha is a Nopp44/46-associated kinase. Competition assays revealed that, unlike most CK2s, TbCK2alpha discriminates highly between ATP and GTP. This distinction may be associated with the substitution of glutamic acid and alanine for the di-asparagine motif thought to participate in purine interaction.