Pea (Pisum sativum L.) seed isolectins 1 and 2 and pea root lectin result from carboxypeptidase-like processing of a single gene product.
The complete amino acid sequences of the alpha-subunits of pea (Pisum sativum L.) seed and root lectin, the C-terminal amino acids of the beta-subunits of pea seed lectin, and most of the sequence of the beta-subunit of pea root lectin were determined. In contrast to earlier reports it was shown that the beta-subunits of both seed isolectins end at Asn-181. The alpha 1 subunits end at Gln-241 (major fraction) or Lys-240 (minor fraction), whereas the alpha 2 subunits end at Ser-239, Ser-238, Ser-237 or Thr-236. psl cDNA clones from seed are identical to psl cDNA clones from root, and root PSL is identical to seed PSL2, ending at Ser-239, Ser-238 or Ser-237. It seems that the presence of Lys-240 is the sole determinant of the charge difference between pea isolectins. PSL1 can be converted into PSL2 by carboxypeptidase P from Penicillium janthinellum. These results confirm that PSL from roots is encoded by the same gene as PSL from seeds. Thus, it seems that, next to an Asn-X specific protease responsible for the processing at positions 181/182 and 187/188, a carboxypeptidase is responsible for the conversion of PSL1 and PSL2, which is probably the final processing product.
Hoedemaeker
F J
FJ
Institute of Molecular Plant Sciences, Leiden University, Netherlands.
Richardson
M
M
Díaz
C L
CL
de Pater
B S
BS
Kijne
J W
JW
D000595:Amino Acid Sequence; D001483:Base Sequence; D002268:Carboxypeptidases / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D018076:DNA, Complementary; D007887:Fabaceae / Q000201:enzymology / Q000235:genetics*; D007525:Isoelectric Focusing; D037102:Lectins / Q000378:metabolism*; D008969:Molecular Sequence Data; D037121:Plant Lectins; D010946:Plants, Medicinal; D011499:Protein Processing, Post-Translational; D012639:Seeds / Q000378:metabolism
D018076:DNA, Complementary; D037102:Lectins; D037121:Plant Lectins; D002268:Carboxypeptidases