Subunit of glucosidase 2, which cleaves sequentially the 2 innermost alpha-1,3-linked glucose residues from the Glc(2)Man(9)GlcNAc(2) oligosaccharide precursor of immature glycoproteins in the endoplasmic reticulum (ER). Specifically required for the cleavage of the final glucose. The subunit beta retains the catalytic subunit alpha in the ER. Heterodimer of a catalytic subunit alpha (gls2) and a subunit beta (gtb1). The N-terminal conserved region (G2B region) is required for the interaction with gls2 and its translocation to the endoplasmic reticulum, whereas the C-terminal conserved region (MRH region) is involved in the recognition of N-glycans bearing from 5 to 9 mannose units. Truncated N-terminus.