Sensory neuropathy-causing mutations in ATL3 cause aberrant ER membrane tethering

Abstract

The ER is a complex network of sheets and tubules that is continuously being remodeled. The relevance of this membrane dynamics is underscored by the fact that mutations in Atlastins (ATL), the ER fusion proteins in mammals, cause neurodegeneration. How defects in this process disrupt neuronal homeostasis is largely unknown. Here we show by EM volume reconstruction of transfected cells, neurons and patient fibroblasts that the HSAN-causing ATL3 mutants promote aberrant ER tethering hallmarked by bundles of laterally attached ER tubules. In vitro, these mutants cause excessive liposome tethering, recapitulating the results in cells. Moreover, ATL3 variants retain their dimerization-dependent GTPase activity, but are unable to promote membrane fusion, suggesting a defect on an intermediate step of the ATL3 functional cycle. Our data therefore show that the effects of ATL3 mutations on ER network organization stretch beyond a loss of fusion, shedding a new light on neuropathies caused by atlastin defects.