Journal of Experimental Botany, Vol. 52, No. 358, pp. 911-917,
May 1, 2001
© 2001 Oxford University Press
Original Papers |
Deglycosylation is necessary but not sufficient for activation of proconcanavalin A
Laboratoire des Transports Intracellulaires, CNRS-UMR 6037, European Institute for Peptide Research (IFRMP No. 23), Université de Rouen, 76821 Mont Saint Aignan, France
Concanavalin A (ConA), one of the most studied plant lectins, is formed in jack bean (Canavalia ensiformis) seeds. ConA is synthesized as an inactive glycoprotein precursor proConA. Different processing events such as endoproteolytic cleavages, ligation of peptides and deglycosylation of the precursor are required to generate the different polypeptides constitutive of mature ConA. Among these events, deglycosylation of the prolectin appears as a key step in the lectin activation. The detection of deglycosylated proConA in immature jack bean seeds indicates that endoproteolytic cleavages are not prerequisite for its deglycosylation. Both the structure of the lectin precursor N-glycans Man89GlcNAc2 and the capacity of Endo H to cleave these oligosaccharide from native proConA in vitro favoured Endo H-type glycosidases as candidates for proConA deglycosylation in planta. Evidence for pH-dependent changes in the prolectin folding were obtained from analysis of the N-glycan accessibility and activation of the deglycosylated lectin precursor in acidic conditions. These data are consistent with the observation that both deglycosylation and acidification of the pH are the minimum requirements to convert the inactive precursor into an active lectin.
Key words: Concanavalin A, lectin activity, endoglycosidase.
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