Biology subjects

Tafur, L.

Publications and source records attributed to Tafur, L..

3 recordsLinked to original sources

bioRxiv2025

Structural basis for TORC2 activation

The Target of Rapamycin Complex 2 (TORC2) is a central node in signaling feedback loops serving to maintain biophysical homeostasis of the plasma membrane (PM). How TORC2 is regulated by mechanical perturbation of the PM is not well understood. To address this, we determined the cryo-electron microscopy structure of endogenous yeast TORC2 to up to 2.2 [A] resolution. Our model refines the position and interactions of TORC2-specific subunits, providing a structural basis for the differential assembly of Tor2 into TORC2. Furthermore, we observe the insertion of the pleckstrin-homology domain of the Avo1 subunit into the Tor2 active site, providing a regulatory mechanism by phosphoinositides. Structure-guided functional experiments reveal a potential TORC2 membrane binding surface and a positively charged pocket in the Avo3 subunit that is necessary for TORC2 activation. Collectively, our data suggest that signaling phosphoinositides activate TORC2 by membrane-induced structural rearrangements via concerted action of conserved regulatory subunits.

biochemistry↗

bioRxiv2024

Structure and function of the yeast amino acid-sensing SEAC-EGOC supercomplex

The Seh1-associated complex (SEAC) transduces amino acid signals to the Target of Rapamycin Complex 1 (TORC1), a master regulator of cell growth located on the vacuole membrane. The SEAC acts as a GTPase activating protein (GAP) for Gtr1, a small GTPase that forms a heterodimer with Gtr2, and as part of the EGO complex (EGOC), relays nutrient signals to TORC1. The SEAC is composed of two subcomplexes, SEACIT, an inhibitor of TORC1 that contains the GAP activity, and SEACAT, that has been proposed to regulate the activity of SEACIT. However, molecular details of its regulation are unclear. Here, we determined the cryo-electron microscopy structure of the SEAC-EGOC supercomplex and studied its function in TORC1 amino acid signalling. A single SEAC can interact with two EGOC molecules via SEACIT, binding exclusively to the "active" version of the EGOC as their interaction depends on Gtr1 being loaded with GTP. SEACAT does not modulate nor interact with the EGOC. The GAP activity of the SEAC is essential for the regulation of TORC1 by amino acids, and its loss phenocopies the lack of Gtr1-Gtr2, establishing the SEAC-EGOC complex as an amino acid-sensing hub. Despite being located far from the active site, deletion of Sea2, or its N-terminal {beta}-propeller domain, also results in defects in amino acid signalling to TORC1. We propose that the SEAC-EGOC supercomplex integrates coatomer-like mechanisms of regulation via bidirectional feedback between GAP-GTPase (SEACIT-EGOC) and coat (SEACAT) modules that explain the functional interaction between Sea2 and the GAP activity. Given the conservation between the SEAC and its mammalian ortholog GATOR, we envision that this mechanism is similar in different organisms.

biochemistry↗

bioRxiv2018

Structural rearrangement of TFIIS- and TFIIF/TFIIE-like subunits in RNA polymerase I transcription complexes

RNA polymerase (Pol) I is a 14-subunit enzyme that solely transcribes pre-ribosomal RNA. Cryo-EM structures of Pol I initiation and elongation complexes have given first insights into the molecular mechanisms of Pol I transcription. Here, we present cryo-electron microscopy structures of yeast Pol I elongation complexes (ECs) bound to the nucleotide analog GMPCPP at 3.2 to 3.4 [A] resolution that provide additional insight into the functional interplay between the TFIIE/TFIIF-like A49-A34.5 heterodimer and the TFIIS-like subunit A12.2 present in Pol I. Strikingly, most of the nucleotide-bound ECs lack the A49-A34.5 heterodimer and adopt a Pol II-like conformation, in which the A12.2 C-terminal domain is bound in a previously unobserved position at the A135 surface. Our work suggests a regulatory mechanism of Pol I transcription where the association of the A49-A34.5 heterodimer to Pol I is regulated by subunit A12.2, thereby explaining in vitro biochemical and kinetic data.

molecular biology↗