The ubiquitous gp63-like metalloprotease from lower trypanosomatids: in the search for a function

Plant and insect trypanosomatids constitute the "lower trypanosomatids", which have been used routinely as laboratory models for biochemical and molecular studies because they are easily cultured under axenic conditions, and they contain homologues of virulence factors from the classic human trypanosomatid pathogens. Among the molecular factors that contribute to Leishmania spp. virulence and pathogenesis, the major surface protease, alternatively called MSP, PSP, leishmanolysin, EC 3.4.24.36 and gp63, is the most abundant surface protein of Leishmania promastigotes. A myriad of functions have been described for the gp63 from Leishmania spp. when the metacyclic promastigote is inside the mammalian host. However, less is known about the functions performed by this molecule in the invertebrate vector. Intriguingly, gp63 is predominantly expressed in the insect stage of Leishmania, and in all insect and plant trypanosomatids examined so far. The gp63 homologues found in lower trypanosomatids seem to play essential roles in the nutrition as well as in the interaction with the insect epithelial cells. Since excellent reviews were produced in the last decade regarding the roles played by proteases in the vertebrate hosts, we focused in the recent developments in our understanding of the biochemistry and cell biology of gp63-like proteins in lower trypanosomatids.

Tripanossomatídeos de insetos e de plantas são informalmente denominados de "tripanossomatídeos inferiores". Estes microrganismos são utilizados rotineiramente como modelos para estudos de bioquímica e de biologia molecular porque são facilmente cultivados sob condições axênicas e porque possuem homólogos aos fatores de virulência encontrados nos tripanossomatídeos que são patógenos humanos clássicos. Dentre os fatores moleculares que contribuem para a virulência e patogênese de Leishmania spp. destaca-se a principal protease de superfície, também conhecida como MSP, PSP, leishmanolisina, EC 3.4.24.36 e gp63, que é a proteína de superfície mais abundante encontrada nas formas promastigotas de Leishmania. Diversas funções foram descritas para a gp63 de Leishmania no hospedeiro vertebrado. Entretanto, pouco é conhecido sobre as funções desempenhadas por essa molécula no inseto vetor. Curiosamente, a gp63 é predominantemente expressa na forma evolutiva de Leishmania encontrada no inseto, e em todos os tripanossomatídeos de insetos e plantas analisados até o presente momento. Os homólogos da gp63 presentes nos tripanossomatídeos inferiores desempenham um papel essencial na nutrição assim como na interação com as células epiteliais do inseto. Uma vez que revisões de excelente qualidade foram produzidas na última década sobre a função de proteases nos hospedeiros vertebrados, nesta revisão nós abordamos os recentes progressos sobre os aspectos bioquímicos e as prováveis funções biológicas desempenhadas pelas proteínas homólogas à gp63 nos tripanossomatídeos inferiores.

Phosphorylation of proteins in virulent promastigotes from Leishmania major

Protein kinases are present in the plasma membrane of the human parasite Leishmania. A marked increase in enzyme activity has been detected as cultures entered into the stationary phase of growth. Since avirulent parasites can be separated from virulent forms by the peanut agglutinin (PNA), we have examined the change in the protein kinase activity of L. major during growth in vitro and the difference in phosphorylation with virulent promastigotes (PNA-) of L. major. Marked similarities were found between the phosphorylation patterns of the logarithmic and stationary phase promastigotes of L. major. On the other hand, when the phosphorylation pattern of those proteins, shared by both the metacyclic (PNA-) promastigotes and the stationary phase cells, was examined, a marked increase in both the total number of phosphoproteins and the extent of their phosphorylation was observed in PNA-. Both the increase in protein kinase activity in the stationary phase parasites and the marked changes in phosphorylation in the highly infective promastigotes, may provide a clue as to the adaptative mechanism which enable promastigotes to survive within the vertebrate host