Caracterização estrutural e funcional da proteína Rqc1p de Saccharomyces cerevisiae e avaliação do seu papel nas vias de resposta a estresses celulares

Abstract

Cellular stress conditions promote proteome remodeling to allow cells to adapt to ever changing environmental conditions. In this context, protein turnover and degradation of defective proteins play a crucial role in removing substandard proteins from cells. Thus, protein surveillance and quality control mechanisms that detect aberrant protein synthesis and prevent their accumulation are essential for maintaining cellular proteostasis. One such surveillance mechanism is the ribosome-associated protein quality control (RQC), which targets newly synthesized defective polypeptides stalled on the ribosome, marking them for degradation via the ubiquitin-proteasome system. In the absence of RQC complex proteins, proteotoxic stress is observed in yeast, while neurodegeneration occurs in mice. Rqc1p is a subunit of the RQC complex, but its function remains poorly understood. In this study, we performed structural and functional characterization of the Saccharomyces cerevisiae Rqc1 protein and investigated its role in the response to both translational and heat shock stresses. In silico analyses revealed that Rqc1p is conserved among eukaryotes and that the polybasic region in the N-terminal and the TCF25 domain play essential roles in its biological function in both the nucleus and the cytoplasm. Moreover, subcellular localization predictions suggest that the polybasic region mediates the nuclear translocation of Rqc1p and may be associated with its function as a transcription factor. Phenotypic analyses showed that RQC1 deletion led to increased sensitivity to heat shock stress and reduced the maximum specific growth rate in this condition. Notably, complementation of RQC1-deficient cells with an expression vector containing this gene was able to restore the wild-type phenotype. Our findings expand the understanding of Rqc1p’s biological role and suggest new ways for investigating its function in protein homeostasis during cellular stress response.