The N-terminal propeptide of the precursor to sporamin acts as a vacuole-targeting signal even at the C terminus of the mature part in tobacco cells.
An asparagine-proline-isoleucine-arginine-leucine (NPIRL) and its related sequences in the N-terminal propeptides (NTPP) of several plant vacuolar proteins, including that of sporamin from sweet potato (SPO) function as vacuole-targeting determinants in a manner that is distinct from the vacuole-targeting determinant in the CTPPs of other plant vacuolar proteins. When the mutant precursor to sporamin, SPO-NTPP (in which NTPP was moved to the C terminus of the mature part), was expressed in tobacco (Nicotiana tabacum) cells, the pro-form was efficiently targeted to the vacuole and the NTPP was cleaved off. Unlike the results obtained with the wild-type precursor, substitution of the NPIRL sequence in the C-terminally located NTPP to asparagine-proline-glycine-arginine-leucine in the SPO-isoleucine-28-to-glycine mutant resulted in missorting of less than 20% of the pro-form to the medium. Unlike the vacuolar transport of SPO-NTPP, the vacuolar transport of SPO-isoleucine-28-to-glycine was strongly inhibited by 33 microM wortmannin, which is similar to the C-terminal propeptide-mediated vacuolar transport. These results suggest that the vacuole-targeting function of the NPIRL sequence is not strictly dependent on its location at the N terminus of a protein and that the C-terminally located mutant NTPP acquired some physicochemical properties of the C-terminal vacuole-targeting sequence.
Koide
Y
Y
Laboratory of Biochemistry, School of Agricultural Sciences, Nagoya University, Japan.
Hirano
H
H
Matsuoka
K
K
Nakamura
K
K
D000595:Amino Acid Sequence; D000730:Androstadienes / Q000494:pharmacology; D017931:DNA Primers; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010940:Plant Proteins / Q000096:biosynthesis* / Q000737:chemistry; D010947:Plants, Toxic; D010957:Plasmids; D016133:Polymerase Chain Reaction; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000737:chemistry / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction; D014026:Nicotiana / Q000502:physiology*; D014617:Vacuoles / Q000187:drug effects / Q000502:physiology*; D000077191:Wortmannin
D000730:Androstadienes; D017931:DNA Primers; D004791:Enzyme Inhibitors; D010446:Peptide Fragments; D010940:Plant Proteins; D011498:Protein Precursors; D011994:Recombinant Proteins; C067142:sporamin protein, Ipomoea batatas; D000077191:Wortmannin