Potato lectin: A three-domain glycoprotein with novel hydroxyproline-containing sequences and sequence similarities to wheat-germ agglutinin

Potato (Solanum tuberosum) tuber lectin is a chitin-binding, hydroxyproline-rich glycoprotein, which may be involved in the defence mechanisms of the plant. We had previously obtained evidence that it consists of at least two very dissimilar domains. The aim was to use a combination of accurate determinations of molecular weight and protein sequencing to gain more accurate information on the domains. Accurate determinations of the molecular weight of the lectin by a MALDI mass spectrometer have shown that the subunit molecular weight is 65500 ( +/- 1100) and that of a totally deglycosylated sample is 31250 (+/- 30). This means that the lectin is 52.3(+/- 1)% carbohydrate with a considerable number of glycoforms being present. Partial sequences rind other analyses are consistent with the existence of three distinct domains. These are: (1) air N-terminal region which is rich in proline but poor in hydroxyproline; (2) a glycosylated region with a glycosylated molecular weight of 45300 (+/- 1100) and a deglycosylated molecular weight of 11050 (+/- 50) which is extremely rich in glycosylated hydroxyproline residues with a similar sequence to extensins; and (3) a cystine-rich domain which has the sugar binding site shows partial conservation of a repeated moth common to many chitin-binding proteins of the hevin family including wheat-germ agglutinin. The closest similarity seems to be to the sequence of potato basic chitinase. Copyright (C) 1996 Elsevier Science Ltd