Analysis of Functional Domains in Rho5, the Yeast Homolog of Human Rac1 GTPase, in Oxidative Stress Response.

Carolin Sterk,Hans-Peter Schmitz,Lauren Gräber,Jürgen J Heinisch

doi:10.3390/ijms20225550

Carolin Sterk, Hans-Peter Schmitz + Show 2 more

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https://doi.org/10.3390/ijms20225550

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Abstract

The small GTPase Rho5 of Saccharomyces cerevisiae is required for proper regulation of different signaling pathways, which includes the response to cell wall, osmotic, nutrient, and oxidative stress. We here show that proper in vivo function and intracellular distribution of Rho5 depends on its hypervariable region at the carboxyterminal end, which includes the CAAX box for lipid modification, a preceding polybasic region (PBR) carrying a serine residue, and a 98 amino acid–specific insertion only present in Rho5 of S. cerevisiae but not in its human homolog Rac1. Results from trapping GFP-Rho5 variants to the mitochondrial surface suggest that the GTPase needs to be activated at the plasma membrane prior to its translocation to mitochondria in order to fulfil its role in oxidative stress response. These findings are supported by heterologous expression of a codon-optimized human RAC1 gene, which can only complement a yeast rho5 deletion in a chimeric fusion with RHO5 sequences that restore the correct spatiotemporal distribution of the encoded protein.

Highlights

The necessity to react to changing environmental conditions has led to the establishment of complex but largely conserved signal transduction pathways in all eukaryotic cells from yeast to humans
These results indicate that the basic character of the polybasic region (PBR) region is required for proper plasma membrane (PM) association of Rho5 and influences the association of Rho5 with mitochondria under oxidative stress, whereas the serine residue appears to be of minor importance
For Rac1, a human homolog of yeast Rho5, a puzzling variety of physiological functions has been reported, which to a large extent may be mediated by what was defined as a hyper-variable region (HVR) at the C-terminal end of ras homology (Rho)-type GTPases

Summary

Introduction

The necessity to react to changing environmental conditions has led to the establishment of complex but largely conserved signal transduction pathways in all eukaryotic cells from yeast to humans. Many of those pathways use monomeric G-proteins of the Ras superfamily as molecular switches, which are active in their GTP-bound and inactive in their GDP-bound state and serve as central and highly conserved components [1]. Guanine nucleotide dissociation inhibitors (GDIs) stabilize the GDP-bound state by preventing the association with GEFs and simultaneously sequester the GTPase from its membrane compartment [3]. The importance of the Ras-type GTPases is reflected in a variety of diseases associated with their malfunctions, ranging from developmental disorders and modulation of the immune system to neurodegenerative diseases (for further reading, see references in studies [4,5])

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