Large alkyl side-chains of isoleucine and leucine in the NPIRL region constitute the core of the vacuolar sorting determinant of sporamin precursor

Plant Mol Biol. 1999 Dec;41(6):825-35. doi: 10.1023/a:1006357413084.


The N-terminal propeptide of the sporamin precursor contains vacuolar targeting information within the Asn-26/Pro-27/Ile-28/Arg-29/Leu-30 (NPIRL) sequence. An Agrobacterium-mediated transient expression assay with tobacco BY-2 cells was employed to investigate the role of each amino acid of the NPIRL region in vacuolar targeting. Replacement of Asn-26, Pro-27, Ile-28 and Leu-30 with several amino acids caused secretion of the mutant prosporamin. Leu was the only amino acid that could be substituted for Ile-28 without affecting transport. Exchange of Leu-30 for amino acids with small side-chains abolished vacuolar delivery. These results indicate that the consensus composition of the NPIRL sequence is [preferably Asn]-[not acidic]-[Ile or Leu]-[any amino acid]-[large and hydrophobic] and suggest that the large alkyl side-chains of Ile-28 and Leu-30 constitute the core of the vacuolar sorting determinant.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Agrobacterium tumefaciens / genetics
  • Agrobacterium tumefaciens / growth & development
  • Amino Acid Sequence
  • Amino Acid Substitution
  • Biological Transport
  • Cells, Cultured
  • Hydrolysis
  • Isoleucine / chemistry*
  • Leucine / chemistry*
  • Mutation
  • Plant Proteins / chemistry
  • Plant Proteins / metabolism*
  • Plants, Toxic
  • Protein Precursors / chemistry
  • Protein Precursors / metabolism*
  • Protein Sorting Signals / metabolism
  • Structure-Activity Relationship
  • Tobacco / cytology
  • Tobacco / microbiology
  • Transformation, Genetic
  • Vacuoles / metabolism*


  • Plant Proteins
  • Protein Precursors
  • Protein Sorting Signals
  • sporamin protein, Ipomoea batatas
  • Isoleucine
  • Leucine