Structural Biology & Biochemistry Theme Seminars

Molecular basis of auto-inhibition, activation and substrate recognition of SARM1, the executioner of axon degeneration

(presented by Dr Weixi Gu)

Programmed axon degeneration represents a pathological feature of many neurodegenerative diseases. The central executioner of this process is SARM1, whose activation triggers injury-induced axon death. We seek to understand the mechanism of SARM1 function, permitting drug development against a range of neurodegenerative diseases.

SARM1 contains an N-terminal ARM domain, two central tandem SAM domains and a C-terminal TIR domain. It exists as octamers in solution, with oligomerization mediated by the SAM domains. The TIR domain unexpectedly possesses NADase activity, essential for subsequent axon death. The ARM domain regulates SARM1 activation by sensing the changes of the activator NMN/ the inhibitor NAD ratio in the axons. Our cryo-EM structure of SARM1 reveals that SARM1 is held in the inactive ring-shaped octamers, with ARM domains directly interacting with the TIR domains to prevent TIR domain assembly. Upon injury, NMN binding to the ARM domain leads to a more compact conformation, disrupting the ARM:TIR interaction and releasing the TIR domains. With the help of a small-molecule NAD analogue, we enabled to capture the active assembly of TIR domains, revealing two antiparallel, head-to-tail strands. 

Together, our results explain the mechanisms of SARM1 auto-inhibition, activation and substrate recognition and present a foundation for drug development.

Biography

I majored in Molecular Biology at the University of Queensland and completed my Master degree in 2015. My interests in the field of immunology and structural biology lead me to continue my studies by pursuing a PhD under the supervision of Prof. Bostjan Kobe, studying the structural and functional characterisations of SARM1, an executioner of axon degeneration. From 2021, I am employed as a postdoctoral research fellow in the Kobe lab, continuing my SARM1 project and also taking on a new COVID-19-related project.

Co-encapsulation of Ancestral P450 and its redox partner Cytochrome P450 reductase in VLP (P22)

(presentd by Loic Bourdon)

The superfamily of enzymes, cytochromes P450 are of interest to the pharmaceutical industry as biocatalysts since they catalyze a large diversity of reactions. The reliance on this enzyme at the industrial scale is affected by various factors, including the need for electron donor partner enzymes, stability (thermo-related, solvent-related), and catalytic efficiency. This Ph.D. project aims to develop reproducible methods for the co-encapsulation of resurrected thermostable ancestral P450s and their natural redox partner, NADPH-cytochrome P450 reductase (CPR) inside virus-like particles (VLPs). The final Virus-Like Particle construct will then be tested against a range of compounds of interest used in the industry and compared to the system currently used for implementing P450s as biocatalysts, i.e., P450s expressed in recombinant bacterial membranes.

Biography

PhD Student Loïc Bourdon is a French Biotechnologist which completed a bachelor on industrial biotechnology followed by a dual major master focused on Agro/Food industry Biotechnology and Applied blue biotechnology in the University of La Rochelle (France). After having set foot in diverse research fields, from the characterization of biocatalysts involved in prebiotics production to the extraction of anti-cancerous compounds from Actinomycetes to the production optimisation of carotenoids from Microalgae. His research project within the University of Queensland is at the Crossroads between the major family of biocatalyst P450 and biocatalyst immobilization, to diversify P450 potential industrial application.