Effect of Deletions of the Genes Encoding Pho3p and Bgl2p on Polyphosphate Level, Stress Adaptation, and Attachments of These Proteins to Saccharomyces cerevisiae Cell Wall.

Inorganic polyphosphates (polyP), according to literature data, are involved in the regulatory processes of molecular complex of the Saccharomyces cerevisiae cell wall (CW). The aim of the work was to reveal relationship between polyP, acid phosphatase Pho3p, and the major CW protein, glucanosyltransglycosylase Bgl2p, which is the main glucan-remodelling enzyme with amyloid properties. It has been shown that the yeast cells with deletion of the PHO3 gene contain more high molecular alkali-soluble polyP and are also more resistant to exposure to alkali and manganese ions compared to the wild type strain. This suggests that Pho3p is responsible for hydrolysis of the high molecular polyP on the surface of yeast cells, and these polyP belong to the stress resistance factors. The S. cerevisiae strain with deletion of the BGL2 gene is similar to the Δpho3 strain both in the level of high molecular alkali-soluble polyP and in the increased resistance to alkali and manganese. Comparative analysis of the CW proteins demonstrated correlation between the extractability of the acid phosphatase and Bgl2p, and also revealed a change in the mode of Bgl2p attachment to the CW of the strain lacking Pho3p. It has been suggested that Bgl2p and Pho3p are able to form a metabolon or its parts that connects biogenesis of the main structural polymer of the CW, glucan, and catabolism of an important regulatory polymer, polyphosphates.

Mitochondria-targeted 1,4-naphthoquinone (SkQN) is a powerful prooxidant and cytotoxic agent.

An increase in the production of reactive oxygen species (ROS) in mitochondria due to targeted delivery of redox active compounds may be useful in studies of modulation of cell functions by mitochondrial ROS. Recently, the mitochondria-targeted derivative of menadione (MitoK3) was synthesized. However, MitoK3 did not induce mitochondrial ROS production and lipid peroxidation while exerting significant cytotoxic action. Here we synthesized 1,4-naphthoquinone conjugated with alkyltriphenylphosphonium (SkQN) as a prototype of mitochondria-targeted prooxidant, and its redox properties, interactions with isolated mitochondria, yeast cells and various human cell lines were investigated. According to electrochemical measurements, SkQN was more active redox agent and, due to the absence of methyl group in the naphthoquinone ring, more reactive as electrophile than MitoK3. SkQN (but not MitoK3) stimulated hydrogen peroxide production in isolated mitochondria. At low concentrations, SkQN stimulated state 4 respiration in mitochondria, decreased membrane potential, and blocked ATP synthesis, being more efficient uncoupler of oxidative phosphorylation than MitoK3. In yeast cells, SkQN decreased cell viability and induced oxidative stress and mitochondrial fragmentation. SkQN killed various tumor cells much more efficiently than MitoK3. Since many tumors are characterized by increased oxidative stress, the use of new mitochondria-targeted prooxidants may be a promising strategy for anticancer therapy.