A carboxyl-terminal propeptide is necessary for proper sorting of barley lectin to vacuoles of tobacco.
Barley lectin is synthesized as a preproprotein with a glycosylated carboxyl-terminal propeptide (CTPP) that is removed before or concomitant with deposition of the mature protein in vacuoles. Expression of a cDNA clone encoding barley lectin in transformed tobacco plants results in the correct processing, maturation, and accumulation of active barley lectin in vacuoles [Wilkins, T.A., Bednarek, S.Y., and Raikhel, N.V. (1990). Plant Cell 2, 301-313]. The glycan of the propeptide is not essential for vacuolar sorting, but may influence the rate of post-translational processing [Wilkins, T.A., Bednarek, S.Y., and Raikhel, N.V. (1990). Plant Cell 2, 301-313]. To investigate the functional role of the CTPP in processing, assembly, and sorting of barley lectin to vacuoles, a mutant barley lectin cDNA clone lacking the 15-amino acid CTPP was prepared. The CTPP deletion mutant of barley lectin was expressed in tobacco protoplasts, suspension-cultured cells, and transgenic plants. In all three systems, the wild-type barley lectin was sorted to vacuoles, whereas the mutant barley lectin was secreted to the incubation media. Therefore, we conclude that the carboxyl-terminal domain of the barley lectin proprotein is necessary for the efficient sorting of this protein to plant cell vacuoles.
Bednarek
S Y
SY
Department of Energy Plant Research Laboratory, Michigan State University, East Lansing 48824-1312.
Wilkins
T A
TA
Dombrowski
J E
JE
Raikhel
N V
NV
D000595:Amino Acid Sequence; D001483:Base Sequence; D001692:Biological Transport; D006056:Golgi Apparatus / Q000378:metabolism; D001467:Hordeum / Q000378:metabolism*; D037102:Lectins / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D037121:Plant Lectins; D010947:Plants, Toxic; D011498:Protein Precursors / Q000378:metabolism; D021382:Protein Sorting Signals / Q000378:metabolism*; D017385:Sequence Homology; D014026:Nicotiana / Q000378:metabolism*; D014170:Transformation, Genetic; D014617:Vacuoles / Q000378:metabolism*
D037102:Lectins; D037121:Plant Lectins; D011498:Protein Precursors; D021382:Protein Sorting Signals