J. Biol. Chem., Vol. 261, Issue 22, 10021-10024, 08, 1986
Characterization of the endoplasmic reticulum-associated precursor of concanavalin A. Partial amino acid sequence and lectin activity
MJ Chrispeels, PM Hartl, A Sturm and L Faye
Concanavalin A (ConA), which is not a glycoprotein, is synthesized as a
glycoprotein precursor (pro-ConA) which is post-translationally processed.
This processing results in the loss of a small glycopeptide with a high
mannose oligosaccharide. Carrington et al. (Carrington, D.M., Auffret, A.,
and Hanke, D.E. (1985) Nature 313, 64-66) determined the nucleotide
sequence of a cDNA for pro-ConA, and in the derived amino acid sequence the
only glycosylation site is in the middle of the molecule. Furthermore, the
derived amino acid sequence of the putative precursor of ConA was found not
to be colinear with that of ConA. Here we show that pro-ConA is located
primarily in an endoplasmic reticulum- rich organelle fraction. Pro-ConA
was purified from this fraction and subjected to amino acid sequencing. The
first 12 amino acids at the N- terminal end of pro-ConA correspond to amino
acids 119-130 of mature ConA, and to amino acids 30-41 of the putative
pre-pro-ConA, the sequence of which was derived from the nucleotide
sequence of a cDNA. Amino acid sequencing of a tryptic glycopeptide with
the high mannose side chain showed that the first 17 amino acids of this
peptide correspond to amino acids 154-170 of pre-pro-ConA. The last six
amino acids in this series correspond to the first six amino acids of
mature ConA. These data fully support the hypothesis of Carrington et al.
that the biosynthesis of ConA involves a post-translational peptide
cleavage, transposition, and ligation within the original polypeptide.
Pro-ConA from the organelle fraction does not bind to Sephadex G-50,
indicating that it has no lectin activity. The processing of pro-ConA
apparently imparts biological activity to this lectin.