title: Identification and evolution of fungal mitochondrial tyrosyl-tRNA synthetases with group I intron splicing activity.
abstract: The bifunctional Neurospora crassa mitochondrial tyrosyl-tRNA synthetase (CYT-18 protein) both aminoacylates mitochondrial tRNA(Tyr) and acts as a structure-stabilizing splicing cofactor for group I introns. Previous studies showed that CYT-18 has distinct tRNA(Tyr) and group I intron-binding sites, with the latter formed by three small "insertions" in the nucleotide-binding fold and other structural adaptations compared with nonsplicing bacterial tyrosyl-tRNA synthetases. Here, analysis of genomic sequences shows that mitochondrial tyrosyl-tRNA synthetases with structural adaptations similar to CYT-18's are uniquely characteristic of fungi belonging to the subphylum Pezizomycotina, and biochemical assays confirm group I intron splicing activity for the enzymes from several of these organisms, including Aspergillus nidulans and the human pathogens Coccidioides posadasii and Histoplasma capsulatum. By combining multiple sequence alignments with a previously determined cocrystal structure of a CYT-18/group I intron RNA complex, we identify conserved features of the Pezizomycotina enzymes related to group I intron and tRNA interactions. Our results suggest that mitochondrial tyrosyl-tRNA synthetases with group I intron splicing activity evolved during or after the divergence of the fungal subphyla Pezizomycotina and Saccharomycotina by a mechanism involving the concerted differentiation of preexisting protein loop regions. The unique group I intron splicing activity of these fungal enzymes may provide a new target for antifungal drugs.
authors.affiliation: Institute for Cellular and Molecular Biology, Department of Chemistry and Biochemistry, and Section of Molecular Genetics and Microbiology, School of Biological Sciences, University of Texas, Austin, TX 78712, USA.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Paukstelis
authors.forename: Alan M
authors.initials: AM
authors.lastname: Lambowitz
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000935:Antifungal Agents / Q000737:chemistry / Q000494:pharmacology; D001233:Aspergillus nidulans / Q000201:enzymology / Q000235:genetics; D003045:Coccidioides / Q000201:enzymology / Q000235:genetics; D017124:Conserved Sequence; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006658:Histoplasma / Q000201:enzymology / Q000235:genetics; D007438:Introns / Q000235:genetics*; D008928:Mitochondria / Q000201:enzymology; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009492:Neurospora crassa / Q000201:enzymology / Q000235:genetics; D011487:Protein Conformation; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D014443:Tyrosine / Q000378:metabolism; D014448:Tyrosine-tRNA Ligase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D000935:Antifungal Agents; D005656:Fungal Proteins; D024101:Mitochondrial Proteins; D012331:RNA, Fungal; D014443:Tyrosine; D014448:Tyrosine-tRNA Ligase