Abstract of the PDB Structure's related Publication:
The yeast KEOPS protein complex comprising Kae1, Bud32, Cgi121, Pcc1 and Gon7 is responsible for the essential tRNA threonylcarbamoyladenosine (t(6)A) modification. Deletion of genes coding for the KEOPS subunits also affects telomere elongation and transcriptional regulation. In the present work, the crystal structure of Bud32/Cgi121 in complex with ADP revealed that ADP is bound in the catalytic site of Bud32 in a canonical manner characteristic of Protein Kinase A (PKA) family proteins. We found that Gon7 forms a stable heterodimer with Pcc1 and report the crystal structure of the Pcc1-Gon7 heterodimer. Gon7 interacts with the same Pcc1 region engaged in the archaeal Pcc1 homodimer. We further show that yeast KEOPS, unlike its archaeal counterpart, exists as a heteropentamer in which Gon7, Pcc1, Kae1, Bud32 and Cgi121 also adopt a linear arrangement. We constructed a model of yeast KEOPS that provides structural insight into the role of Gon7. The model also revealed the presence of a highly positively charged crater surrounding the entrance of Kae1 that likely binds tRNA.
Kinase, Endopeptidase, and other Protein of Small size (KEOPS) protein complex consists of the five Bud32, Cgi121, Kae1, and Pcc1 hetero-pentamer protein complex (Zhang et al. 2015 ). Interestingly, this complex is universally conserved among Archaea and Eukarya, despite being absent in bacteria (Daugeron et al. 2011 ). Differently from the archaeal counterpart, eukaryotic KEOPS adopt a linear arrangement in its five protein components (Zhang et al. 2015 ). Cgi121 works in a genetic pathway and interacts with Bud32 (Bianchi & Shore, 2006 ). Telomeres are regions placed at the end of chromosomes composed of repetitive nucleotide sequences and specialized proteins. They organize chromosome replication and are involved in the recruitment of telomeres (Bianchi & Shore, 2006 ), thereby providing the essential cellular chromosome-end protection, and preserving telomere homeostasis (Daugeron et al. 2011 ). Specifically, the deletion of Cgi121, or other KEOPS components, leads to short telomeres. This implies the failure to add telomeres de novo to DNA double-strand breaks. Physiologically, KEOPS complex, moreover, promotes both telomere uncapping ad telomere elongation (Bianchi & Shore, 2006 ). Cgi121 and Bud32 form a protein complex with ADP that binds to the catalytic site of Bud32. This bond is arranged in the typical manner of the Protein Kinase A (PKA) protein family (Zhang et al. 2015 ). KEOPS is moreover required for the formation of a threonylcarbamoyl group on adenosine at position 37 (t637A) in all tRNAs that read ANN codons (Wan et al. 2016 ). Nevertheless, Cgi121 is not required for tRNA modification.
A genome-wide screen identifies the evolutionarily conserved KEOPS complex as a telomere regulator.
Downey M, Houlsworth R, Maringele L, Rollie A, Brehme M, Galicia S, Guillard S, Partington M, Zubko MK, Krogan NJ, Emili A, Greenblatt JF, Harrington L, Lydall D, Durocher D