Structural characterization of a xylanase from psychrophilic yeast by massspectrometry

The complete structural characterization of the xylanase, a glycoprotein co nstituted of 338 amino acids, from psychrophilic antarctic yeast Criptococc us albidus TAE85 was achieved both at the protein and carbohydrate level by exploiting mass spectrometric procedures. The verification of the primary structure, the definition of the S-S pattern, the assignment of glycosglati on sites and the investigation of glycosylation pattern were performed. Thi s analysis revealed the occurrence of N-glycosylation only at Asn254, modif ied by high-mannose structure; moreover the protein resulted to be O-glycos ylated with GalGalNAc structures. The data obtained on both the N- and O-li nked glycans in the cold xylanase constitute the first description of the g lycosylation pattern in psychrophylic microorganisms and suggest that the g lycosylation system in cold-adapted organisms might have similarities as we ll as differences with respect to mesophylic and thermophylic cells, The cy steine pairings were eventually identified as Cys173-Cys205 and Cys272-Cys2 78, with Cys89 showing a free thiol group. These data suggest that a common folding motif might occur within the entire xylanase family in which the s econd Cys is linked to the third one with the fourth and fifth joined toget her.