Temperature, organic solvent and pH stabilization of the neutral protease from Salinovibrio proteolyticus: significance of the structural calcium.

In order to clarify the impact of Ca-binding sites (Ca1 and 2) on the conformational stability of neutral proteases (NPs), we have analyzed the thermal, pH and organic solvent stability of a NP variant, V189P/A195E/G203D/A268E (Q-mutant), from Salinovibrio proteolyticus. This mutant has shown to bind calcium more tightly than the wild-type (WT) at Ca1 and to possess Ca2. Q-mutant was resisted against autolysis, thermoinactivation and pH denaturation in a Ca-dependent manner and exhibited better activity in organic solvents compared to the WT enzyme. These results imply that Ca1 and Ca2 are important for the conformational stability of NPs.

Heterologous production of polyunsaturated fatty acids in Saccharomyces cerevisiae causes a global transcriptional response resulting in reduced proteasomal activity and increased oxidative stress.

Due to their health benefits there is much interest in developing microbial processes for efficient production of polyunsaturated fatty acids (PUFAs). In this study we co-expressed Mucor rouxii Δ(12) - and Δ(6) -desaturase genes in Saccharomyces cerevisiae, which resulted in a yeast strain that accumulated linoleic acid and γ-linolenic acid in the different lipid species. Additionally, the strain contained higher levels of phospholipids and lower levels of ergosterol than the reference strain. Integrated analysis of the transcriptome revealed decreased expression of genes involved in ergosterol biosynthesis, but more unexpectedly it also pointed towards attenuated activity of the ubiquitin-proteasome system and a reduced oxidative stress response. In vitro and in vivo measurements showed reduced levels of all three proteasomal activities and also increased levels of reactive oxidative species in the PUFA-producing strain. Overall our results clearly show that PUFAs in yeast can be detrimental for several key cellular pathways, such as the oxidative stress response and proteasomal activity, suggesting that the membrane composition is of vital importance for these processes.