Exoglycosidase that cleaves the single beta-linked mannose residue from the non-reducing end of all N-linked glycoprotein oligosaccharides. Hydrolysis of terminal, non-reducing beta-D-mannose residues in beta-D-mannosides. Optimum pH is 5. Glycan metabolism; N-glycan degradation. Monomer. Detected in kidney (at protein level) (PubMed:1556126). Found in spleen and to a lesser extent in liver. Not detected in kidney or brain. N-glycosylated. Defects in MANBA cause beta-mannosidosis, a severe disorder that affects peripheral and central nervous system myelin resulting in tremor, nystagmus, ataxia and early death. The primary storage products associated with the enzyme deficiency are the trisaccharide Man-beta-1-4-GlcNAc-beta-1-4-GlcNAc and the disaccharide Man-beta-1-4-GlcNAc. Belongs to the glycosyl hydrolase 2 family.