The structural basis for SARM1 inhibition and activation under energetic stress

Abstract
Data availability
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Abstract

SARM1 an executor of axonal degeneration, displays NADase activity that depletes the key cellular metabolite, NAD+, in response to nerve injury. The basis of SARM1 inhibition, and its activation under stress conditions are still unknown. Here, we present cryo-EM maps of SARM1 at 2.9 and 2.7 Å resolution. These indicate that SARM1 homo-octamer avoids premature activation by assuming a packed conformation, with ordered inner and peripheral rings, that prevents dimerization and activation of the catalytic domains. This inactive conformation is stabilized by binding of SARM1's own substrate NAD+ in an allosteric location, away from the catalytic sites. This model was validated by mutagenesis of the allosteric site, which led to constitutively active SARM1. We propose that the reduction of cellular NAD+ concentration contributes to the disassembly of SARM1's peripheral ring, which allows formation of active NADase domain dimers, thereby further depleting NAD+ to cause an energetic catastrophe and cell death.

Data availability

Coordinates and structure factors have been deposited in the Protein Data Bank with accession numbers 6ZFX, 7ANW, 6ZG0, 6ZG1, and in the EMDB with accession numbers 11187, 11834, 11190, 11191 for the GraFix-ed, NAD+ supplemented, not treated, and SAM1-2 models and maps, respectively.

The following data sets were generated

1. Sporny M
2. Guez-Haddad J
3. Khazma T
4. Yaron A
5. Mim C
6. Isupov MN
7. Zalk R
8. Dessau M
9. Hons M
10. Opatowsky Y
(2020) hSARM1 GraFix-ed
Protein Data Bank, 6ZFX.

https://www.rcsb.org/structure/6ZFX
1. Sporny M
2. Guez-Haddad J
3. Khazma T
4. Yaron A
5. Mim C
6. Isupov MN
7. Zalk R
8. Dessau M
9. Hons M
10. Opatowsky Y
(2020) hSARM1 NAD+ complex
Protein Data Bank, 7ANW.

https://www.rcsb.org/structure/7ANW
1. Sporny M
2. Guez-Haddad J
3. Khazma T
4. Yaron A
5. Mim C
6. Isupov MN
7. Zalk R
8. Dessau M
9. Hons M
10. Opatowsky Y
(2020) SARM1 SAM1-2 domains
Protein Data Bank, 6ZG0.

https://www.rcsb.org/structure/6ZG0
1. Sporny M
2. Guez-Haddad J
3. Khazma T
4. Yaron A
5. Mim C
6. Isupov MN
7. Zalk R
8. Dessau M
9. Hons M
10. Opatowsky Y
(2020) SARM1 SAM1-2 domains
Protein Data Bank, 6ZG1.

https://www.rcsb.org/structure/6ZG1

Article and author information

Author details

Michael Sporny

Life Sciences, Bar Ilan University, Ramat Gan, Israel

Competing interests
The authors declare that no competing interests exist.
Julia Guez-Haddad

Life Sciences, Bar Ilan University, Ramat Gan, Israel

Competing interests
The authors declare that no competing interests exist.
Tami Khazma

Life Sciences, Bar Ilan University, Ramat Gan, Israel

Competing interests
The authors declare that no competing interests exist.
Avraham Yaron

Department of Biomolecular Sciences, The Weizmann Institute of Science, Rehovot, Israel

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0001-9340-7245
Moshe Dessau

Azrieli Faculty of Medicine, Bar Ilan University, Safed, Israel

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0002-1954-3625
Yoel Shkolnisky

Department of Applied Mathematics, Tel-Aviv University, Tel-Aviv, Israel

Competing interests
The authors declare that no competing interests exist.
Carsten Mim

Dept. For Biomedical Engineering and Health Systems, Royal Technical Institute (KTH), Stockholm, Sweden

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0001-6402-8270
Michail N Isupov

Biosciences, University of Exeter, Exeter, United Kingdom

Competing interests
The authors declare that no competing interests exist.
Ran Zalk

National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer-Sheva, Israel

Competing interests
The authors declare that no competing interests exist.
Michael Hons

Grenoble Outstation, European Molecular Biology Laboratory, Grenoble, France

Competing interests
The authors declare that no competing interests exist.
Yarden Opatowsky

Life Sciences, Bar Ilan University, Ramat Gan, Israel

For correspondence
yarden.opatowsky@biu.ac.il

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0002-9609-1204

Funding

Israel Science Foundation (1425/15)

Yarden Opatowsky

Israel Science Foundation (909/19)

Yarden Opatowsky

I declare that the funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Copyright

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.