Dessau, M. | bioRxiv Science

bioRxiv2025

Monoclonal Antibodies from COVID-19 Convalescent Patients Target Cryptic Epitopes for Universal SARS-CoV-2 Neutralization

The COVID-19 pandemic, which has resulted in over seven million global fatalities, poses a substantial threat to public health and precipitated a global economic crisis. Emerging variants of concern (VOCs) with enhanced transmissibility and improved immune evasion may compromise the efficacy of current antiviral and immunotherapies, necessitating comprehensive investigations into the immune response to SARS-CoV-2. The conformational dynamics of the receptor binding domain (RBD) in SARS-CoV-2 spike and the presentation of neutralizing antibody epitopes influence viral transmission and infection rates. In this study, we have identified highly conserved non-RBM epitopes for two potent monoclonal antibodies (mAbs), TAU-1109 and TAU-2310, isolated from convalescent human patients, which contribute to the broad neutralizing activity of these mAbs against all the circulating VOCs, including the recently emerged Omicron subvariants. We employed high- resolution structural data in conjunction with systematic biochemical investigation to elucidate the neutralization mechanism of TAU-1109 and TAU-2310. The mechanism involves antibody-mediated destabilization of the spike trimer, resulting in the premature shedding of the S1 subunit and rendering the spike incapable of mediating host cell entry. The identification of conserved cryptic epitopes in our study advances the mechanistic understanding of immune response against SARS-CoV-2, providing novel avenues for the development of universal therapeutic antibodies and vaccines to combat COVID-19.

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↗