Structural analysis of the SAM domain of the Arabidopsis mitochondrial tRNA import receptor

Bence Olasz, Luke Smithers, Genevieve Evans, Anandhi Anandan, Monika Murcha, Alice Vrielink

Research output: Contribution to journalArticlepeer-review

Abstract

Mitochondria are membrane bound organelles of endosymbiotic origin with limited protein coding capacity. The import of nuclear-encoded protein and nucleic acids is required and essential for maintaining organelle mass, number and activity. As plant mitochondria do not encode all the necessary tRNA types required, the import of cytosolic tRNA is vital for organelle maintenance. Recently, two mitochondrial outer membrane proteins, named Tric1 and Tric2, for tRNA import component, were shown to be involved in the import of cytosolic tRNA. Tric1/2 binds tRNA ala via conserved residues in the C-terminal Sterile Alpha Motif (SAM) domain. Here we report the X-ray crystal structure of the Tric1 SAM domain. We identified the ability of the SAM domain to form a helical superstructure with 6 monomers per helical turn and key amino acid residues responsible for its formation. We determined that the oligomerization of Tric1 SAM domain may play a role in protein function whereby mutation of Gly241 introducing a larger side chain at this position disrupted the oligomer and resulted in the loss of RNA binding capability. Furthermore, complementation of Arabidopsis thaliana Tric1/2 knockout lines with a mutated Tric1 failed to restore the defective plant phenotype. AlphaFold2 structure prediction of both the SAM domain and Tric1 support a cyclic pentameric or hexameric structure. In the case of a hexameric structure a pore of sufficient dimensions to transfer tRNA across the mitochondrial membrane is observed. Our results highlight the importance of oligomerization of Tric1 for protein function.

Original languageEnglish
Article number107258
Pages (from-to)107258
JournalThe Journal of Biological Chemistry
Volume300
Issue number5
Early online dateApr 2024
DOIs
Publication statusPublished - May 2024

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