Structural basis for membrane remodelling by the AP5:SPG11-SPG15 complex

Abstract

The human spastizin (spastic paraplegia 15, SPG15) and spatacsin (spastic paraplegia 11, SPG11) complex is involved in cargo sorting from late endosomes to the Golgi, and mutations in these two proteins are linked with hereditary autosomal recessive spastic paraplegia (HSP). SPG11-SPG15 can cooperate with evolutionarily ancient fifth adaptor protein complex (AP5). We employed cryo-electron microscopy and in silico predictions to investigate the structural assemblies of SPG11-SPG15 and AP5:SPG11-SPG15 complex. The W-shaped SPG11-SPG15 intertwined in a head-to-head fashion, and the N-terminal region of SPG11 is required for AP5 complex interaction and assembly. The AP5 complex is in a super open conformation. We employed in vitro lipid binding assays and cellular localization analysis to investigate AP5:SPG11-SPG15 membrane binding properties. Here we solve a major problem in understanding AP5:SPG11-SPG15 function in autophagic lysosome reformation (ALR), using a fully reconstituted system. We reveal that the AP5:SPG11-SPG15 complex binds PI3P molecules, can sense membrane curvature and drive membrane remodelling in vitro. These studies provide key insights into the structure and function of the spastic paraplegia AP5:SPG11-SPG15 complex, which is essential for the initiation of autolysosome tubulation.