Evidências para a presença de uma proteína receptora de IP3 em células de Saccharomyces cerevisiae.

O bombeamento de prótons é um processo executado pela H+-ATPase de membrana plasmática Pma1p e é importante em Saccharomyces cerevisiae pois permite a captação de nutrientes através da criação de gradiente eletroquímico. Em presença de glicose esta enzima é ativada. Estudos preliminares mostram uma forte relação entre a presença de IP3, a liberação de cálcio vacuolar e ativação de Pma1p. Para a elucidação da via de liberação de cálcio faz-se necessária a identificação de proteínas receptoras de IP3 e suas relações que culminam neste processo. Com este objetivo nosso trabalho adotou duas estratégias independentes: a utilização de ensaio de afinidade seguida de tentativa de identificação por espectrometria de massas; e utilização de bancos de dados e recursos de bioinformática contígua a avaliações bioquímicas para uma identificação indireta através das interações descritas para Yvc1p, proteína responsável pela saída de cálcio. Na primeira estratégia, verificamos que os prováveis receptores de IP3 apresentam peso molecular entre 66 e 97 kDa, porém ainda não obtivemos a identificação por espectrometria de massas; na segunda estratégia, porém, chegamos a um grupo de seis proteínas (Yvc1p, Alg6p, Nmd2p, Mdm10p, Sse2p e Swc3p ) que estão relacionadas a liberação do cálcio vacuolar e que apresentam o peso molecular entre 66 e 97 kDa.The pumping proton is a process carried out by the plasma membrane H+-ATPase Pma1p and is important in Saccharomyces cerevisiae since it allows the uptake of nutrients through the formation of electrochemical gradient. In the presence of glucose this enzyme is activated. Preliminary studies show a strong correlation between the presence of IP3, the release of intracellular calcium and activation of Pma1p. To elucidate the pathway of calcium release it is necessary to identify IP3 receptors and their relationship that culminate in this process. In this work we adopted our goal of two independent strategies: the use of affinity assay followed by identification tentative by mass spectrometry, and use of databases and contiguous bioinformatics resources to biochemical evaluations for indirect identification through interactions described for Yvc1p, protein responsible for the output of calcium from vacuole. In the first strategy, we found that likely IP3 receptors have molecular weights between 66 and 97 kDa, but not yet obtained the mass spectrometry identification. In the latter strategy, however, we come to a group of six proteins (Yvc1p, Alg6p, Nmd2p, Mdm10p, Sse2p and Swc3p) that are related to vacuolar calcium output and that present molecular weight between 66 and 97 kDa

Lpx1p links glucose-induced calcium signaling and plasma membrane H+-ATPase activation in Saccharomyces cerevisiae cells.

In yeast, as in other eukaryotes, calcium plays an essential role in signaling transduction to regulate different processes. Many pieces of evidence suggest that glucose-induced activation of plasma membrane H+-ATPase, essential for yeast physiology, is related to calcium signaling. Until now, it was not identified any protein that could be regulated by calcium in this context. Lpx1p, a serine-protease that is also involved in the glucose-induced activation of the plasma membrane H+-ATPase activation, could be a candidate to respond to intracellular calcium signaling involved in this process. In this work, and by using different approaches, we showed many pieces of evidence suggesting that the requirement of calcium signaling for activation of the plasma membrane H+-ATPase is due to its requirement for activation of Lpx1p. According to the current model, activation of Lpx1p would cause hydrolysis of an acetylated tubulin that keeps the plasma membrane H+-ATPase in an inactive state. Therefore, after its activation, Lpx1p would hydrolyze the acetylated tubulin making the plasma membrane H+-ATPase phosphorylation accessible for at least one protein kinase

Lpx1p links glucose-induced calcium signaling and plasma membrane H+-ATPase activation in Saccharomyces cerevisiae cells

In yeast, as in other eukaryotes, calcium plays an essential role in signaling transduction to regulate different processes. Many pieces of evidence suggest that glucose-induced activation of plasma membrane H+-ATPase, essential for yeast physiology, is related to calcium signaling. Until now, no protein that could be regulated by calcium in this context has been identified. Lpx1p, a serine-protease that is also involved in the glucose-induced activation of the plasma membrane H+-ATPase, could be a candidate to respond to intracellular calcium signaling involved in this process. In this work, by using different approaches, we obtained many pieces of evidence suggesting that the requirement of calcium signaling for activation of the plasma membrane H+-ATPase is due to its requirement for activation of Lpx1p. According to the current model, activation of Lpx1p would cause hydrolysis of an acetylated tubulin that maintains the plasma membrane H+-ATPase in an inactive state. Therefore, after its activation, Lpx1p would hydrolyze the acetylated tubulin making the plasma membrane H+-ATPase accessible for phosphorylation by at least one protein kinase