The C‐terminal sequence from common bugle leaf galactan:galactan galactosyltransferase is a non‐sequence‐specific vacuolar sorting determinant

The Ajuga reptans L. galactan:galactan galactosyltransferase (ArGGT) is a vacuolar enzyme that synthesizes long‐chain raffinose family oligosaccharides (RFOs), the major storage carbohydrates of this plant. ArGGT is structurally and functionally related to acid plant α‐galactosidases (α‐Gals) of the glycosylhydrolase family 27, present in the apoplast or the vacuole. Sequence comparison of acid α‐Gals with ArGGT revealed that they all contain an N‐terminal signal sequence and a highly similar core sequence. Additionally, ArGGT and some acid α‐Gals contain C‐terminal extensions with low sequence similarities to each other. Here, we show that the C‐terminal pentapeptide, SLQMS, is a non‐sequence‐specific vacuolar sorting determinant. Analogously, we demonstrate that the C‐terminal extensions of selected acid α‐Gals from Arabidopsis, barley, and rice, are also non‐sequence‐specific vacuolar sorting determinants, suggesting the presence of at least one vacuolar form of acid α‐Gal in every plant species.