Identification of MIOREX complex proteins of unknown function which may be involved in mitochondrial translation.

Author(s)

Jhulia Almeida Clarck Chagas

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Ciências Biomédicas (ICB/SDI)
• Defense date: 2022-04-28

Examining board members

Mário Henrique de Barros; Marilis do Valle Marques; Luis Eduardo Soares Netto; Marcelo Afonso Vallim

• Advisor: Mário Henrique de Barros

Abstract

Mitochondria are essential organelles for cell function and responsible for oxidative phosphorylation in eukaryotic organisms. Along evolution, mitochondrial genomes differentiated into different kingdoms with little variation in their content. The existence of this genetic system is vital for the morphogenesis of a competent respiratory organelle and for translating information genetic through its own set of mitoribosomes. Saccharomyces cerevisiae has been used as a study model for mitochondrial biogenesis for over fifty years, having great value in the identification and characterization of proteins that affect mitochondrial function. Recent studies have demonstrated the presence of a large complex in yeast called MIOREX, which includes the mitoribosome and proteins involved in posttranscriptional gene expression steps. Many components of this complex still have an unknown function and have been named Mrx proteins. In this work, we over-express MIOREX components screening for those with altered phenotypes that may help functional characterization. The MRX9 gene was selected in this screening. A tagged version of Mrx9p allowed its submitochondrial localization, the protein is imported into mitochondria, located intrinsically in the inner membrane facing the matrix. The excess of Mrx9p is harmful to the mitochondria of S. cerevisiae, as it leads to low rates of COX1 mRNA translation, in addition to providing the defective version of this protein. Cox1p is a subunit of complex IV (cytochrome c oxidase) of the electron respiratory chain. The mrx9 null mutant does not show any growth deficiencies in media that assess mitochondrial activity or difficulties in translating or accumulating mitochondrial polypeptides. However, the strains that overexpress MRX9 showed phenotypes of reduced activities for complex IV, in addition to having a delay in the adaptation of respiratory growth at the end of the fermentative metabolism. Studies in strains without introns in the mitochondrial genome showed that the defect in the translation of Cox1p in strains that have an excess of Mrx9p does not occur, thus, there is a relationship between the phenotype and the presence of these non-coding regions. Furthermore, the overexpression of MRX9 has been shown to alter the accessibility of Mss51p to the mitoribosome. Mss51p acts in the initiation and elongation of COX1 translation, in addition to participating in the assembly of this subunit in the inner membrane of the organelle. Finally, the results of this work indicated a role of Mrx9p in the COX1 translation process; however, further studies will be necessary to unveil Mrx9p regulatory mechanism in the MIOREX complex. (AU)

• FAPESP's process: 20/01573-8 - Study of proteins of the MIOREX complex with unknown function putatively involved with the mitochondrial translation
• Grantee: Jhulia Almeida Clarck Chagas
• Support Opportunities: Scholarships in Brazil - Master