Biology subjects

Opatowsky, Y.

Publications and source records attributed to Opatowsky, Y..

3 recordsLinked to original sources

bioRxiv2022

A Duplex Structure of SARM1 Octamers Induced by a New Inhibitor

In recent years, there has been growing interest in SARM1 as a potential breakthrough drug target for treating various pathologies of axon degeneration. SARM1-mediated axon degeneration relies on its TIR domain NADase activity, but recent structural data suggest that the non-catalytic ARM domain could also serve as a pharmacological site as it has an allosteric inhibitory function. Here, we screened for synthetic small molecules that inhibit SARM1 by stabilizing the ARM-dependent inactive, compact octamer ring conformation, and tested a selected set of these compounds in a DRG axon degeneration assay. Using cryo-EM, we found that one of the newly discovered inhibitors, a Calmidazolium designated TK106, not only stabilizes the previously reported inhibited conformation of the octamer, but also promotes the formation of a meta-stable structure: a duplex of octamers (16 protomers), which we have now determined to 4.0 [A] resolution. In the duplex, each ARM domain protomer is not only engaged in lateral interactions with neighboring protomers but is further stabilized by contralateral contacts with the opposing octamer ring. Mutagenesis of the duplex contact sites leads to SARM1 activation in cultured cells. Based on our data we propose that the duplex assembly constitutes an additional auto-inhibition mechanism that tightly prevents pre-mature activation and axon degeneration.

biochemistry↗

bioRxiv2020

The Structural Basis for SARM1 Inhibition, and Activation Under Energetic Stress

SARM1 is a central executor of axonal degeneration (1). Mechanistically, SARM1 contains NADase activity, which, in response to nerve injury, depletes the key cellular metabolite, NAD+ (2-5). Interestingly, SARM1 knockout mouse models do not present any apparent physiological impairment. Yet, the lack of SARM1 protects against various neuropathies (6, 7), thereby highlighting SARM1 as a likely safe and effective drug target (8). However, the absence of a SARM1 structure, in its active or inhibited form, makes it impossible to understand the molecular basis of SARM1 inhibition, and its activation under stress conditions. In this study we present two cryo-EM maps of SARM1 (at 2.6 [A] and 2.9 [A] resolution). We show that the inhibited SARM1 homo-octamer assumes a packed conformation with well-ordered inner and peripheral rings. Here the catalytic TIR domains are held apart from each other and are unable to form dimers, which is a prerequisite for NADase activity. More importantly, after screening several cellular metabolites we discovered that the inactive conformation is stabilized by the binding of SARM1s own substrate: NAD+. The NAD+ inhibitory allosteric site is located away from the NAD+ catalytic site of the TIR domain. Site-directed mutagenesis of the allosteric site leads to constitutive active SARM1. Based on our data we propose that a reduction of cellular NAD+ concentrations (an early indication of disease-associated and age-related neurodegeneration (9)) disassemble SARM1s peripheral ring, which allows NADase activity. This leads to an energetic catastrophe and eventually cell death. The discovery of the allosteric inhibitory site opens the door for the development of effective drugs that will prevent SARM1 activation, rather than compete for binding to the NADase catalytic site. Brief descriptionIt is not known how NAD+ depletion brings about neurodegeneration. Here, we show that the intrinsic NADase activity of SARM1 is allosterically inhibited by physiological concentrations of NAD+. NAD+ stabilizes a compact, auto-inhibited conformation of the SARM1 octamer. Once NAD+ levels are depleted, the allosteric inhibition is released, enabling SARM1s NADase activity, which eventually leads to energetic catastrophe and cell death.

biochemistry↗

bioRxiv2019

Sema3A Facilitates a Retrograde Death Signal via CRMP4-Dynein Complex Formation in ALS Motor Axons

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease with selective dysfunction; it causes the death of motor neurons (MNs). In spite of some progress, currently no effective treatment is available for ALS. Before such treatment can be developed, a more thorough understanding of ALS pathogenesis is required. Recently, we demonstrated that ALS-mutated muscles contribute to ALS pathology via secretion of destabilizing factors such as Sema3A; these factors trigger axon degeneration and Neuromuscular Junction (NMJ) disruption. Here, we focus on the molecular mechanism by which muscle contribute to MNs loss in ALS. We identified CRMP4 as part of a retrograde death signal generated in response to muscle-secreted Sema3A, in ALS-diseased MNs. Exposing distal axons to Sema3A induces CRMP4-dynein complex formation and MN loss in both mouse (SOD1G93A) and human-derived (C9orf72) ALS models. Introducing peptides that interfere with CRMP4-dynein interaction in MN axons profoundly reduces Sema3A-dependent MN loss. Thus, we discovered a novel retrograde death signal mechanism underlying MN loss in ALS.\n\nSummaryMaimon et al. identify a novel retrograde death mechanism that contribute to MN loss in ALS, in which CRMP4-Dynein complex is form and retrogradely move along the axon.

neuroscience↗