Sequence Analysis of Grape (Vitis vinifera) Berry Chitinases That Cause Haze Formation in Wines

Chitinases account for ca. 50% of the soluble proteins in the berries of the grape vine ( Vitis vinifera L. Muscat of Alexandria). The other major proteins present are thaumatin-like proteins. Both these groups of proteins persist through the vinification process and cause hazes and sediments in bottled wines. Four chitinases have been purified from Muscat of Alexandria fruit and characterized by both sequence and mass spectral analysis. Their protein sequences were highly similar, and all proteins were modified at their N-terminus. It was confirmed for three of the chitinases that the N-terminal group was a pyroglutamate residue. Comparative sequence analysis of two chitinases from berries and two from wine demonstrated that, despite their reputed resistance to proteolytic degradation, some limited proteolytic processing of these proteins occurs. The peptide fragments of the chitinases account for only 3% of the total soluble protein content of the fruit.