Different site-specific N-glycan types in wheat (Triticum aestivum L.) PAP phytase.

Phytase activity in grain is essential to make phosphate available to cell metabolism, and in food and feed. Cereals contain the purple acid phosphatase type of phytases (PAPhy). Mature wheat grain is dominated by TaPAPhy_a which, in the present work, has been characterized by extensive peptide and glycopeptide sequencing by mass spectrometry. Seven N-linked glycosylation sites were found. Three of these sites were dominated by variant forms of the XylMan(3)FucGlcNAc(2), i.e. the HRP-type of glycan. Complex-type glycans with one or two additional GlcNAc were observed, however in trace amounts only. At four sites the glycan consisted of a single GlcNAc residue. The mature protein is ca. 500 residues in size and appears to be truncated at the N- and C-termini.