InstructThe latest webinar in the Instruct-ERIC Structure Meets Function series will be a special edition. This month, guest speakers from Instruct's partner institutions in Latin America will give talks on the work they completed as part of the International Call. Register for the webinar here.
The international call was conducted in the context of the EU-LAC ResInfra project. This project aims to harbour collaborative efforts between Europe and Latin America and the Caribbean. This has been through access calls, staff exchanges, bi-regional events and more! Find out more about Instruct-ERIC's international collaboration here.
This month will feature two speakers from University of Sao Paulo: Richard Garratt and Italo Cavini!
Watch the previous webinars in the series here.
Time: 3:00pm CEST (2:00pm BST, 10:00am BRT).
Moderator: Maria Natalia Lisa
Talk 1: Protein crystallography off the beaten track: Septins, their filaments and the importance of access to research infrastructure
Speaker: Richard Garratt, University of Sao Paulo, Brazil
Abstract: Septins are GTP-binding proteins which are taken to be the fourth filamentous component of the cytoskeleton and, via membrane association, play roles in a wide range of cellular events including cytokinesis. In humans, 13 different septins spontaneously form hetero-oligomeric particles which obey specific assembly rules and subsequently polymerize into filaments. For the last 15 years we have been using a divide and conquer approach to shed light on the assembly process itself and how it relates to both physiological and pathological processes. Our crystallographic studies have been supported by a plethora of biophysical techniques using research infrastructure from around the world culminating in the determination of the 3D structure of a hexameric septin complex solved by cryo-electron microscopy. During this short talk we will report on the progress made so far, including what the filament structure has taught us about function.
Talk 2: The versatile septin coiled-coil domains
Speaker: Italo Cavini, University of Sao Paulo, Brazil
Abstract: Septins are membrane-associated, GTP-binding proteins present in most eukaryotes that, as part of the cytoskeleton, play important roles as scaffolds and/or diffusion barriers. All these roles are related to their ability to heteropolymerize in organized filament structures like paired filaments, rings and gauzes. In humans, there are 13 septins classified into four groups based on sequence similarity. Septins have mainly three domains: an N-terminal domain (NTD), a more conserved GTP-binding (G-) domain and the C-terminal domain (CTD) which may contain coiled-coil (CC) repeats. Two different parallel CCs are expected to be present within protofilaments: a short-length homodimer, formed by the CTDs of a SEPT2-group member (SEPT1, 2, 4 or 5) and a long-length heterodimer, formed between the CTD of a SEPT6-group member (SEPT6, 8, 10, 11 or 14) and the CTD of SEPT7. The CCs have been related to cross-linking between protofilaments and membrane interaction. We recently uncovered the structure of five different homodimeric human septin coiled coils (Leonardo et al. 2021 JMB). In the SEPT2-group member, by analyzing the orientation of three X-ray CC structures (two antiparallels, one parallel) and conducting solution NMR experiments and in silico modeling, we concluded that these CTDs are “orientationally ambiguous”, being able to switch, given certain conditions, between both orientations. The two other structures are antiparallel homodimers of the CC region of SEPT6 and the CTD of SEPT8. The antiparalelism allowed us to speculate the possibility of antiparallel homodimeric structures as participants of the cross-bridges seen between septin filaments. A new X-ray structure of the heterodimeric CC of SEPT14-SEPT7 is very peculiar and reveals hendecad repeats which could act as a molecular recognition flag, avoiding the interaction with wrong septin partners. In this talk, I will highlight the versatility of the human septin C-terminal domains, a key feature to allow septins to assemble into different filament arrangements.
