Cloning and functional expression of Rpn1, a regulatory-particle non-ATPase subunit 1, of proteasome from Trypanosoma cruzi

Proteasomes from Structure to Function: Perspectives from Archaea

Insight into the world of proteolysis has expanded considerably over the past decade. Energy-dependent proteases, such as the proteasome, are no longer viewed as nonspecific degradative enzymes associated solely with protein catabolism but are intimately involved in controlling biological processes that span life to death. The proteasome maintains this exquisite control by catalyzing the precisely timed and rapid turnover of key regulatory proteins. Proteasomes also interplay with chaperones to ensure protein quality and to readjust the composition of the proteome following stress. Archaea encode proteasomes that are highly related to those of eukaryotes in basic structure and function. Investigations of archaeal proteasomes coupled with those of eukaryotes has greatly facilitated our understanding of the molecular mechanisms that govern regulated protein degradation by this elaborate nanocompartmentalized machine.

Genetic diversity and kinetic properties of Trypanosoma cruzi dihydroorotate dehydrogenase isoforms

Dihydroorotate dehydrogenase (DHOD) is the fourth enzyme in the de novo pyrimidine biosynthetic pathway and is essential in Trypanosoma cruzi, the parasitic protist causing Chagas' disease. T. cruzi and human DHOD have different biochemical properties, including the electron acceptor capacities and cellular localization, suggesting that T. cruzi DHOD may be a potential chemotherapeutic target against Chagas' disease. Here, we report nucleotide sequence polymorphisms of T. cruzi DHOD genes and the kinetic properties of the recombinant enzymes. T. cruzi Tulahuen strain possesses three DHODgenes: DHOD1 and DHOD2, involved in the pyrimidine biosynthetic (pyr) gene cluster on an 800 and a 1000 kb chromosomal DNA, respectively, and DHOD3, located on an 800 kb DNA. The open reading frames of all three DHOD genes are comprised of 942 bp, and encode proteins of 314 amino acids. The three DHOD genes differ by 26 nucleotides, resulting in replacement of 8 amino acid residues. In contrast, all residues critical for constituting the active site are conserved among the three proteins. Recombinant T. cruzi DHOD1 and DHOD2 expressed in E. coli possess similar enzymatic properties, including optimal pH, optimal temperature, Vmax, and Km for dihydroorotate and fumarate. In contrast, DHOD3 had a higher Vmax and Km for both substrates. Orotate competitively inhibited all three DHOD enzymes to a comparable level. These results suggest that, despite their genetic variations, kinetic properties of the three T. cruziDHODs are conserved. Our findings facilitate further exploitation of T. cruzi DHOD inhibitors, as chemotherapeutic agents against Chagas' disease.

Mass spectrometric analysis of expression of ATPase subunits encoded by duplicated genes in the 19S regulatory particle of rice 26S proteasome

The 26S proteasome consisting of a 20S proteasome and a pair of 19S regulatory particles (RP) plays important roles in degradation of the ubiquitinated protein in eukaryotic cells. The RP consists of six different ATPase subunits and, at least, 11 non-ATPase subunits. In rice, we previously identified duplicated genes encoding four ATPase subunits, OsRpt1, OsRpt2, OsRpt4, and OsRpt5. In this study, the genomic sequences of all rice ATPase subunits were identified from the rice genome database and the genomic structure of ATPase subunit genes was determined. The rice RP was purified, and the ATPase subunit isoforms encoded by three pairs of duplicated genes, OsRpt2a/OsRpt2b, OsRpt4a/OsRpt4b, and OsRpt5a/OsRpt5b, were identified in RP by using electrospray ionization quadrupole time-of-flight mass spectrometry. The relative amounts and the expression patterns of these ATPase subunit isoforms in the bran were found to be different from those of the callus, suggesting the presence of multiform 19S regulatory particles engaged in the tissue-specific protein metabolism.

Diversity of aspartate carbamoyltransferase genes of Trypanosoma cruzi

The pyrimidine-biosynthetic (pyr) gene cluster, a tandem array of pyr1-pyr3-pyr6/5-pyr2(ACT)-pyr4 from the 5' terminus, encodes all the six enzymes of de novo pyrimidine biosynthesis and occurs as a polycistronic transcription unit in Trypanosoma cruzi. The gene encoding aspartate carbamoyltransferase (ACT), the second enzyme of the pathway, was characterised using a laboratory-reared Tulahuen strain and Tulahuen-derived clones of T. cruzi. Three loci with different restriction maps that contain ACT1, ACT2, and ACT3 were identified. ACT1 and ACT2 are involved in the pyr gene cluster on two different chromosomal DNA molecules of 1,000 and 800 kb, respectively, whereas ACT3 is linked with pyr4 alone. There are 29 nucleotide substitutions out of 981 positions in these three ACTs, yielding 13 amino acid replacements, and a deletion of triplet nucleotides in ACT1 entails a lack of single amino acid residue. Transcription of the three ACTs takes place in the three developmental stages of the parasite, epimastigotes, trypomastigotes, and amastigotes. Pulsed field gel electrophoresis and Southern blot analyses demonstrated that the cloned T. cruzi stocks, Y-02, CAN III/1, Sylvio-X10/4, and possibly Esmeraldo/3, also possess two complete sets of the pyr gene cluster including ACT, accompanied by additional incomplete clusters. These results suggest that the marked intra-species diversity in the copy number and chromosomal localisations of ACT and other pyr genes may have resulted from partial duplications and subsequent translocations of the polycistronic pyr gene cluster.

Characterization and role of protozoan parasite proteasomes

The proteasome, a large non-lysosomal multi-subunit protease complex, is ubiquitous in eukaryotic cells. In protozoan parasites, the proteasome is involved in cell differentiation and replication, and could therefore be a promising therapeutic target. This article reviews the present knowledge of proteasomes in protozoan parasites of medical importance such as Giardia, Entamoeba, Leishmania, Trypanosoma, Plasmodium and Toxoplasma spp.

Identification of the 19S regulatory particle subunits from the rice 26S proteasome

The 26S proteasome, a protein complex consisting of a 20S proteasome and a pair of 19S regulatory particles (RP), is involved in ATP-dependent proteolysis in eukaryotes. In yeast, the RP contains six different ATPase subunits and, at least, 11 non-ATPase subunits. In this study, we identified the rice homologs of yeast RP subunit genes from the rice expressed sequence tag (EST) library. The complete nucleotide sequences of the homologs for five ATPase subunits, OsRpt1, OsRpt2, OsRpt4, OsRpt5 and OsRpt6, and five non-ATPase subunits, OsRpn7, OsRpn8, OsRpn10, OsRpn11 and OsRpn12, and the partial sequences of one ATPase subunit, OsRpt3, and six non-ATPase subunits, OsRpn1, OsRpn2, OsRpn3, OsRpn5, OsRpn6 and OsRpn9, were determined. Gene homologs of four ATPase subunits, OsRpt1, OsRpt2, OsRpt4 and OsRpt5, and three non- ATPase subunits, OsRpn1, OsRpn2 and OsRpn9, were found to be encoded by duplicated genes. The rice RP was purified by immunoaffinity chromatography with a Protein A column immobilized antibody against rice 20S proteasome, and the subunit composition was determined. The homologs obtained from the rice EST library were identified as genes encoding subunits of RP purified from rice, including the both products of duplicated genes by using electrospray ionization quadrupole time-of-flight mass spectrometry. Post-translational modifications and processing in rice RP subunits were also identified. Various types of RP complex with different subunit compositions are present in rice cells, suggesting the multiple functions of rice proteasome.