RESUMO
Recent advances in molecular genetics of Leishmania parasites prompted us to develop methods of functional genetic complementation in Leishmania and apply them to the isolation of genes involved in the biosynthesis of the virulence determinant LPG, an abundant GPI-anchored polysaccharide. LPG1, the gene product identified by complementation of our R2D2 LPG- mutant, may be a glycosyltransferase responsible for the addition of galactofuranose to the nascent chain. As galactofuranose is not found in mammalian cells, inhibition of the addition of this sugar could be exploited for chemotherapy. Overall, the success of the functional complementation approach opens the way to the identification of a variety of genes involved in pathogenesis and parasitism
Assuntos
Animais , Fosfatidilinositóis/biossíntese , Teste de Complementação Genética , Glicolipídeos/biossíntese , Leishmania donovani/genética , Leishmania/genética , Virulência/genética , Aglutinação , Sequência de Aminoácidos , Anticorpos Monoclonais , Sequência de Bases , Cosmídeos , DNA de Protozoário/genética , DNA de Protozoário/metabolismo , Galactosiltransferases/biossíntese , Biblioteca Gênica , Leishmania donovani/patogenicidade , Leishmania/patogenicidade , Dados de Sequência MolecularRESUMO
The biosynthesis of GM1 ganglioside (Gal beta 1-3GalNAc beta 1-4 (NeuAc alpha 2-3) Gal beta 1-4Glc-Cer) and nLcOse4Cer is catalyzed by two different beta-galactosyltransferases GalT-3 (UDP-Gal: GM2 beta 1-3GalT) and GalT-4 (UDP-Gal: Lc3 beta 1-4GalT) respectively. Solubilized GalT-3 and GalT-4 have been purified 3,000-fold and 22,000-fold, respectively, from 11-19-day-old embryonic chicken brain. The purified GalT-3 transfers galactose to GM2 very actively (Km 33 microM), whereas acetyl GM2 is not an active substrate (Km 350 microM), GalT-3 and GalT-4 are classified as HYCARS (hydrophobic recognition site) and CARS (carbohydrate recognition sites), respectively. An anion-transport inhibitor DIDS (diisothiocyanato stilbene 4,4'-disulphonate), irreversibly inhibits both GalT-3 and GalT-4 activities by binding to a UDP binding site. Polyclonal antibodies against purified GalT-3 and GalT-4 inhibited these two purified activities and showed no cross reactivity on the western blots. RNA-PCR of 11-day-old embryonic chicken brain mRNA with PCR primers designed from the homologous coding regions of cloned sequences of beta 1-4 GalT of human, bovine, and murine-tissues produced a -600 bp cDNA fragment. Dideoxy-sequences of this fragment reveals it to be 74% similar to the nucleotide sequences of the cloned beta 1-4GalT from human liver. The cloned-600 bp cDNA was used to identify two mRNA transcripts (1.4 and 2.3 kb) from ECB by Northern blot analysis and four genomic DNA EcoRI fragments (18.6, 12.9, 10.5 and 3.7 kb) on a Southern blot analysis.