Propeptide of a precursor to a plant vacuolar protein required for vacuolar targeting

Ken Matsuoka, Kenzo Nakamura

Research output: Contribution to journalArticle

192 Citations (Scopus)

Abstract

Sporamin is a protein without glycans that accumulates in large quantities in the vacuoles of the tuberous root of the sweet potato. It is synthesized as a prepro precursor with an N-terminal extension composed of a 21-amino-acid signal peptide and a 16-amino-acid propeptide. A total of 48 base pairs, corresponding to the nucleotide sequence that encodes the propeptide, was deleted from a cDNA clone for sporamin. This Δpro mutant sequence, as well as the sequence of the wild-type sporamin cDNA, was placed downstream from the promoter of the 35S transcript from cauliflower mosaic virus and introduced into the genome of suspension-cultured tobacco cells by Agrobacterium-mediated transformation. In contrast to the vacuolar localization of sporamin in cells that expressed the wild-type precursor, sporamin was secreted into the culture medium from cells in which the Δpro precursor was expressed. The secreted form of sporamin was shorter by two amino acids at its N terminus than authentic sporamin; it migrated anomalously during electrophoresis on SDS/polyacrylamide gel as a result of the presence of intramolecular disulfide bridges, as does authentic sporamin. The kinetics of secretion of sporamin from the cell were similar to those of proteins normally secreted by the host tobacco cells. These results indicate that the propeptide of the precursor to sporamin is required for correct targeting of sporamin to the vacuole and that proteins can be secreted from plant cells by a bulk-flow default pathway in the absence of a functional sorting signal.

Original languageEnglish
Pages (from-to)834-838
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume88
Issue number3
DOIs
Publication statusPublished - Jan 1 1991

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Plant Proteins
Vacuoles
Amino Acids
Tobacco
Complementary DNA
Caulimovirus
Ipomoea batatas
Agrobacterium
Proteins
Plant Cells
Protein Sorting Signals
Base Pairing
Disulfides
Polysaccharides
Culture Media
Electrophoresis
Cultured Cells
Suspensions
Clone Cells
Genome

All Science Journal Classification (ASJC) codes

  • General

Cite this

Propeptide of a precursor to a plant vacuolar protein required for vacuolar targeting. / Matsuoka, Ken; Nakamura, Kenzo.

In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 88, No. 3, 01.01.1991, p. 834-838.

Research output: Contribution to journalArticle

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AB - Sporamin is a protein without glycans that accumulates in large quantities in the vacuoles of the tuberous root of the sweet potato. It is synthesized as a prepro precursor with an N-terminal extension composed of a 21-amino-acid signal peptide and a 16-amino-acid propeptide. A total of 48 base pairs, corresponding to the nucleotide sequence that encodes the propeptide, was deleted from a cDNA clone for sporamin. This Δpro mutant sequence, as well as the sequence of the wild-type sporamin cDNA, was placed downstream from the promoter of the 35S transcript from cauliflower mosaic virus and introduced into the genome of suspension-cultured tobacco cells by Agrobacterium-mediated transformation. In contrast to the vacuolar localization of sporamin in cells that expressed the wild-type precursor, sporamin was secreted into the culture medium from cells in which the Δpro precursor was expressed. The secreted form of sporamin was shorter by two amino acids at its N terminus than authentic sporamin; it migrated anomalously during electrophoresis on SDS/polyacrylamide gel as a result of the presence of intramolecular disulfide bridges, as does authentic sporamin. The kinetics of secretion of sporamin from the cell were similar to those of proteins normally secreted by the host tobacco cells. These results indicate that the propeptide of the precursor to sporamin is required for correct targeting of sporamin to the vacuole and that proteins can be secreted from plant cells by a bulk-flow default pathway in the absence of a functional sorting signal.

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