Activation of the Aspergillus PacC zinc finger transcription factor requires two proteolytic steps.
The Aspergillus PacC transcription factor undergoes proteolytic activation in response to alkaline ambient pH. In acidic environments, the 674 residue translation product adopts a 'closed' conformation, protected from activation through intramolecular interactions involving the < or = 150 residue C-terminal domain. pH signalling converts PacC to an accessible conformation enabling processing cleavage within residues 252--254. We demonstrate that activation of PacC requires two sequential proteolytic steps. First, the 'closed' translation product is converted to an accessible, committed intermediate by proteolytic elimination of the C-terminus. This ambient pH-regulated cleavage is required for the final, pH-independent processing reaction and is mediated by a distinct signalling protease (possibly PalB). The signalling protease cleaves PacC between residues 493 and 500, within a conserved 24 residue 'signalling protease box'. Precise deletion or Leu498Ser substitution prevents formation of the committed and processed forms, demonstrating that signalling cleavage is essential for final processing. In contrast, signalling cleavage is not required for processing of the Leu340Ser protein, which lacks interactions preventing processing. In its two-step mechanism, PacC processing can be compared with regulated intramembrane proteolysis.
Díez
Eliecer
E
Departamento de Microbiología Molecular, Centro de Investigaciones Biológicas del CSIC, Velázquez 144, Madrid 28006, Spain.
Alvaro
Josué
J
Espeso
Eduardo A
EA
Rainbow
Lynne
L
Suárez
Teresa
T
Tilburn
Joan
J
Arst
Herbert N
HN
Peñalva
Miguel A
MA
D000595:Amino Acid Sequence; D000818:Animals; D001233:Aspergillus nidulans / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D010450:Endopeptidases / Q000378:metabolism*; D005656:Fungal Proteins / Q000096:biosynthesis* / Q000235:genetics; D007930:Leucine / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D051381:Rats; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics; D016335:Zinc Fingers
D005656:Fungal Proteins; C092394:PacC protein, Aspergillus; D014157:Transcription Factors; D012694:Serine; D010450:Endopeptidases; D007930:Leucine