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Molecular cloning of a gene encoding an arabinogalactan-protein from pear (Pyrus communis) cell suspension culture

Chen, C.G., Pu, Z.Y., Moritz, R.L., Simpson, R.J., Bacic, A., Clarke, A.E., Mau, S.L.
Proceedings of the National Academy of Sciences of the United States of America 1994 v.91 no.22 pp. 10305-10309
Pyrus communis, complementary DNA, structural genes, glycoproteins, apoproteins, plant proteins, nucleotide sequences, amino acid sequences, cell suspension culture, galactans, arabinose
Arabinogalactan-proteins (AGPs) are proteoglycans containing a high proportion of carbohydrate (typically > 90%) linked to a protein backbone rich in hydroxyproline (Hyp), Ala, Ser, and Thr. They are widely distributed in plants and may play a role in development. The structure of the carbohydrate of some AGPs is known in detail but information regarding the protein backbone is restricted to a few peptide sequences. Here we report isolation and partial amino acid sequencing of the protein backbone of an AGP. This AGP is a member of one of four major groups of AGPs isolated from the filtrate of pear cell suspension culture. A cDNA encoding this protein backbone (145 amino acids) was cloned; the deduced protein is rich in Hyp, Ala, Ser, and Thr, which together account for > 75% of total residues. It has three domains, an N-terminal secretion signal, a central hydrophilic domain containing all of the Pro residues, and a hydrophobic C-terminal domain that is predicted to be a transmembrane helix. Approximately 93% of the Pro residues are hydroxylated and hence are potential sites for glycosylation.