Cryo-EM structure of fission yeast tetrameric α-mannosidase Ams1.

Fungal α-mannosidase Ams1 and its mammalian homolog MAN2C1 hydrolyze terminal α-linked mannoses in free oligosaccharides released from misfolded glycoproteins or lipid-linked oligosaccharide donors. Ams1 is transported by selective autophagy into vacuoles. Here, we determine the tetrameric structure of Ams1 from the fission yeast Schizosaccharomyces pombe at 3.2 Å resolution by cryo-electron microscopy. Distinct from a low resolution structure of S. cerevisiae Ams1, S. pombe Ams1 has a prominent N-terminal tail that mediates tetramerization and an extra β-sheet domain. Ams1 shares a conserved active site with other enzymes in glycoside hydrolase family 38, to which Ams1 belongs, but contains extra N-terminal domains involved in tetramerization. The atomic structure of Ams1 reported here will aid understanding of its enzymatic activity and transport mechanism.