A novel C-terminal sequence from barley polyamine oxidase is a vacuolar sorting signal.
Barley contains two different isoforms of flavin-containing polyamine oxidase (BPAO1 and BPAO2). We have previously demonstrated that BPAO2 is a symplastic protein in barley leaves. On the contrary, maize polyamine oxidase (MPAO), the best characterized member of this enzyme class, is apoplastic. Comparison of the derived amino-acid sequences of BPAO2 and MPAO has revealed that both precursor proteins include a cleavable N-terminal signal peptide of 25 amino acid residues, but the barley enzyme shows an extra C-terminal extension of eight amino acids. By means of MPAO engineering with BPAO2 C-terminal tail (MPAO-T) and exploiting transient expression in Nicotiana tabacum protoplasts, we demonstrate that this oligopeptide is a signal for protein sorting to the plant vacuole. The vacuolar sorting of MPAO-T was saturable. Specific mutations of the C-terminal tail were constructed to determine which amino acid residues of this novel propeptide affect proper protein sorting. No consensus sequence or common structural determinant is required for the intracellular retention of the MPAO-T protein, but a gradual lowering of the efficiency was observed as a result of progressive deletion of the C-terminus.
Dipartimento di Biologia, Università Roma Tre, Viale Guglielmo Marconi 446, 00146 Rome, Italy.
Manuela
M
Cervelli
Oriana
O
Di Caro
Alessandra
A
Di Penta
Riccardo
R
Angelini
Rodolfo
R
Federico
Alessandro
A
Vitale
Paolo
P
Mariottini
D000595:Amino Acid Sequence; D001692:Biological Transport; D004252:DNA Mutational Analysis; D001467:Hordeum / Q000201:enzymology*; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000737:chemistry* / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D030821:Plants, Genetically Modified; D021382:Protein Sorting Signals; D014026:Nicotiana / Q000235:genetics; D014617:Vacuoles / Q000201:enzymology; D003313:Zea mays / Q000201:enzymology; D000097667:Polyamine Oxidase
D000587:Oxidoreductases Acting on CH-NH Group Donors; D010940:Plant Proteins; D021382:Protein Sorting Signals; D000097667:Polyamine Oxidase