Cystatin B and its EPM1 mutants are polymeric and aggregate prone in vivo

Elena Cipollini, Massimo Riccio, Rossella Di Giaimo, Fabrizio Dal Piaz, Giuseppe Pulice, Sandra Catania, Ilaria Caldarelli, Maja Dembic, Spartaco Santi, Marialuisa Melli

Research output: Contribution to journalArticlepeer-review


Progressive myoclonus epilepsy type 1 (EPM1) is a neurodegenerative disease correlating with mutations of the cystatin B gene. Cystatin B is described as a monomeric protein with antiprotease function. This work shows that, in vivo, cystatin B has a polymeric structure, highly resistant to SDS, urea, boiling and sensitive to reducing agents and alkaline pH. Hydrogen peroxide increases the polymeric structure of the protein. Mass spectrometry analysis shows that the only component of the polymers is cystatin B. EPM1 mutants of cystatin B transfected in cultured cells are also polymeric. The banding pattern generated by a cysteine-minus mutant is different from that of the wild-type protein as it contains only monomers, dimers and some very high MW bands while misses components of MW intermediate between 25 and 250 kDa. Overexpression of wild-type or EPM1 mutants of cystatin B in neuroblastoma cells generates cytoplasmic aggregates. The cysteine-minus mutant is less prone to the formation of inclusion bodies. We conclude that cystatin B in vivo has a polymeric structure sensitive to the redox environment and that overexpression of the protein generates aggregates. This work describes a protein with a physiological role characterized by highly stable polymers prone to aggregate formation in vivo.

Original languageEnglish
Pages (from-to)312-322
Number of pages11
JournalBiochimica et Biophysica Acta - Molecular Cell Research
Issue number2
Publication statusPublished - Feb 2008


  • Cellular aggregates
  • Cystatin B
  • Cytoskeleton
  • EPM1
  • Neurodegeneration
  • Polymers

ASJC Scopus subject areas

  • Cell Biology
  • Molecular Biology
  • Biophysics


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