The role of protein phosphorylation in the life cycle of malaria parasites is slowly emerging. Here we combine global phospho-proteomic analysis with kinome-wide reverse genetics to assess the importance of protein phosphorylation in Plasmodium falciparum asexual proliferation. We identify 1177 phosphorylation sites on 650 parasite proteins that are involved in a wide range of general cellular activities such as DnA synthesis, transcription and metabolism as well as key parasite processes such as invasion and cyto-adherence. several parasite protein kinases are themselves phosphorylated on putative regulatory residues, including tyrosines in the activation loop of PfGsK3 and PfCLK3; we show that phosphorylation of PfCLK3 Y526 is essential for full kinase activity. A kinome-wide reverse genetics strategy identified 36 parasite kinases as likely essential for erythrocytic schizogony. These studies not only reveal processes that are regulated by protein phosphorylation, but also define potential anti-malarial drug targets within the parasite kinome.

SummaryEcotin is a potent inhibitor of family S1A serine peptidases, enzymes lacking in the protozoan parasite Leishmania major. Nevertheless, L. major has three ecotin-like genes, termed inhibitor of serine peptidase (ISP). ISP1 is expressed in vectorborne procyclic and metacyclic promastigotes, whereas ISP2 is also expressed in the mammalian amastigote stage. Recombinant ISP2 inhibited neutrophil elastase, trypsin and chymotrypsin with Kis between 7.7 and 83 nM. L. major ISP2-ISP3 double null mutants (Disp2/3) were created. These grew normally as promastigotes, but were internalized by macrophages more efficiently than wild-type parasites due to the upregulation of phagocytosis by a mechanism dependent on serine peptidase activity. Disp2/3 promastigotes transformed to amastigotes, but failed to divide for 48 h. Intracellular multiplication of Disp2/3 was similar to wild-type parasites when serine peptidase inhibitors were present, suggesting that defective intracellular growth results from the lack of serine peptidase inhibition during promastigote uptake. Disp2/3 mutants were more infective than wild-type parasites to BALB/c mice at the early stages of infection, but became equivalent as the infection progressed. These data support the hypothesis that ISPs of L. major target host serine peptidases and influence the early stages of infection of the mammalian host.

Excessive NH 3 production in the rumen is a major nutritional inefficiency in ruminant animals. Experiments were undertaken to compare the rates of NH 3 production from different substrates in ruminal fluid in vitro and to assess the role of asaccharolytic bacteria in NH 3 production. Ruminal fluid was taken from four rumenfistulated sheep receiving a mixed hay-concentrate diet. The calculated rate of NH 3 production from Trypticase varied from 1.8 to 19.7 nmol mg of protein ؊1 min ؊1 depending on the substrate, its concentration, and the method used. Monensin (5 M) inhibited NH 3 production from proteins, peptides, and amino acids by an average of 28% with substrate at 2 mg/ml, compared to 48% with substrate at 20 mg/ml (P ‫؍‬ 0.011). Of the total bacterial population, 1.4% grew on Trypticase alone, of which 93% was eliminated by 5 M monensin. Many fewer bacteria (0.002% of the total) grew on amino acids alone. Nineteen isolates capable of growth on Trypticase were obtained from four sheep. 16S ribosomal DNA and traditional identification methods indicated the bacteria fell into six groups. All were sensitive to monensin, and all except one group (group III, similar to Atopobium minutum), produced NH 3 at >250 nmol min ؊1 mg of protein ؊1 , depending on the medium, as determined by a batch culture method. All isolates had exopeptidase activity, but only group III had an apparent dipeptidyl peptidase I activity. Groups I, II, and IV were most closely related to asaccharolytic ruminal and oral Clostridium and Eubacterium spp. Group V comprised one isolate, similar to Desulfomonas piger (formerly Desulfovibrio pigra). Group VI was 95% similar to Acidaminococcus fermentans. Growth of the Atopobium-and Desulfomonas-like isolates was enhanced by sugars, while growth of groups I, II, and V was significantly depressed by sugars. This study therefore demonstrates that different methodologies and different substrate concentrations provide an explanation for different apparent rates of ruminal NH 3 production reported in different studies and identifies a diverse range of hyper-ammonia-producing bacteria in the rumen of sheep.Deamination of amino acids in the rumen, which leads to the loss of NH 3 across the ruminal wall, is one of the main causes of inefficient N retention by ruminants (23). For many years, it had been assumed that NH 3 formation was carried out by some of the numerically predominant species of ruminal bacteria that had been identified as producing NH 3 weakly from protein or protein hydrolysates (3). However, Russell and his colleagues (7,8,12,35,36) calculated that these bacteria did not have sufficient activity to account for observed in vitro rates of NH 3 production by the mixed population in their cattle, and they isolated bacteria which were much less numerous than the others but which possessed a specific activity of NH 3 production from Trypticase which was an order of magnitude greater than that of the other species. Moreover, these bacteria, unlike the others, were gram positive and highly sen...