Posttranslational modification of an isoinhibitor from the potato proteinase inhibitor II gene family in transgenic tobacco yields a peptide with homology to potato chymotrypsin inhibitor I.
A member of the potato proteinase inhibitor II (PPI-II) gene family under the control of the cauliflower mosaic virus 35S promoter has been introduced into tobacco (Nicotiana tabacum). Purification of the PPI-II protein that accumulates in transgenic tobacco has confirmed that the N-terminal signal sequence is removed and that the inhibitor accumulates as a protein of the expected size (21 kD). However, a smaller peptide of approximately 5.4 kD has also been identified as a foreign gene product in transgenic tobacco plants. This peptide is recognized by an anti-PPI-II antibody, inhibits the serine proteinase chymotrypsin, and is not observed in nontransgenic tobacco. Furthermore, amino acid sequencing demonstrates that the peptide is identical to a lower molecular weight chymotrypsin inhibitor found in potato tubers and designated as potato chymotrypsin inhibitor I (PCI-I). Together, these data confirm that, as postulated to occur in potato, PCI-I does arise from the full-length PPI-II protein by posttranslational processing. The use of transgenic tobacco represents an ideal system with which to determine the precise mechanism by which this protein modification occurs.
McManus
M T
MT
Plant Molecular Genetics Laboratory, Grasslands Research Centre, AgResearch, Palmerston North, New Zealand.
Laing
W A
WA
Christeller
J T
JT
White
D W
DW
D000595:Amino Acid Sequence; D002918:Chymotrypsin / Q000037:antagonists & inhibitors; D008969:Molecular Sequence Data; D005810:Multigene Family; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D010940:Plant Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D030821:Plants, Genetically Modified; D010947:Plants, Toxic; D011480:Protease Inhibitors / Q000737:chemistry*; D011499:Protein Processing, Post-Translational; D017386:Sequence Homology, Amino Acid; D011198:Solanum tuberosum / Q000235:genetics* / Q000378:metabolism; D014026:Nicotiana
D010446:Peptide Fragments; D010940:Plant Proteins; D011480:Protease Inhibitors; C034104:proteinase inhibitor II protein, plant; C023578:proteinase inhibitor I (plants); D002918:Chymotrypsin