Septins are membrane-associated GTP-binding proteins which are important in a wide range of physiologically essential processes such as cytokinesis, microtubule dynamics, formation of diffusion barriers and mechanotransduction. The importance of the coiled-coil domains in the formation and maintenance of septin complexes is still not fully understood. It has been almost 15 years since the release of the first septin X-ray structural model, and no complex structure so far was able to reveal information on the coiled coils probably due to intrinsic flexibility of the hinge which connects their helices to the G-domains. Although some progress has been made with the recent solution of homodimeric septin coiled coils by X-ray diffraction, an important piece of the puzzle is still missing: the structure of the heteromeric coiled coil.This project proposes to obtain structural information on the septin heteromeric coiled-coil domains using nuclear magnetic resonance spectroscopy. The study aims to validate and complement the structures solved (or still to be solved) by X-ray crystallography and/or generated by deep learning-based modeling methods. Inspecting their structure in aqueous solution is crucial in these systems, which can potentially reveal differences compared to in crystallo, as it has occurred with SEPT1CC, SEPT4CC (antiparallel by the X-ray structures whereas parallel by solution NMR) and SEPT6CC/SEPT7CC (crystalline structure from SEPT6CC+SEPT7CC mixture showed only SEPT6CC homodimers). Our main goal is to obtain NMR structural data for the following septin heretomeric coiled coils in solution: (i) at least one from human and (ii) the one from baker's yeast. Human structures accounts for nearly 85% of all septin structures in the PDB and yeast septins are undoubtedly the most studied septin in vivo. We hope to better explain the role played by the coiled coils in the filament arrangements seen in different microscopy studies.
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