SSNA1 stabilizes dynamic microtubules and detects microtubule damage.

Elizabeth J Lawrence,Marija Zanic,Goker Arpag,Cayetana Arnaiz

doi:10.7554/elife.67282

Abstract

Sjögren's syndrome nuclear autoantigen-1 (SSNA1/NA14) is a microtubule-associated protein with important functions in cilia, dividing cells, and developing neurons. However, the direct effects of SSNA1 on microtubules are not known. We employed in vitro reconstitution with purified proteins and TIRF microscopy to investigate the activity of human SSNA1 on dynamic microtubule ends and lattices. Our results show that SSNA1 modulates all parameters of microtubule dynamic instability-slowing down the rates of growth, shrinkage, and catastrophe, and promoting rescue. We find that SSNA1 forms stretches along growing microtubule ends and binds cooperatively to the microtubule lattice. Furthermore, SSNA1 is enriched on microtubule damage sites, occurring both naturally, as well as induced by the microtubule severing enzyme spastin. Finally, SSNA1 binding protects microtubules against spastin's severing activity. Taken together, our results demonstrate that SSNA1 is both a potent microtubule-stabilizing protein and a novel sensor of microtubule damage; activities that likely underlie SSNA1's functions on microtubule structures in cells.

Highlights

Sjogren’s syndrome nuclear autoantigen-1 (SSNA1/NA14) is a microtubule-associated protein (MAP)that plays important roles in cilia, cell division and neuronal development
Our results show that SSNA1 modulates all parameters of microtubule dynamic instability – slowing down the rates of growth, shrinkage and catastrophe, and promoting rescue
We performed a titration of soluble tubulin from 3 μM to 10 μM with and without 2.5 μM SSNA1 and found that SSNA1 promoted templated nucleation compared to the tubulin alone condition, supporting the role of SSNA1 in microtubule nucleation (Figure 1B)

Summary

Introduction

That plays important roles in cilia, cell division and neuronal development. SSNA1 localizes to basal bodies and axonemes where it is required for proper cilium assembly and intraflagellar transport (Lai et al, 2011; Pfannenschmid et al, 2003; Schoppmeier, Mages, & Lechtreck, 2005). SSNA1 is enriched at the spindle poles and midbody, and is necessary for proper cell division (Goyal, Renvoise, Chang, & Blackstone, 2014; Pfannenschmid et al, 2003). SSNA1 promotes axon elongation and branching in developing neurons (Basnet et al, 2018; Goyal et al, 2014). SSNA1 is a small (~14 kDa), coiled-coil protein that self-assembles into higher-order fibrils (Basnet et al, 2018; Ramos-Morales, Infante, Fedriani, Bornens, & Rios, 1998; Rodriguez-Rodriguez et al, 2011)

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