Large proteins have a great tendency to aggregate but a low propensity to form amyloid fibrils

PLoS One. 2011 Jan 13;6(1):e16075. doi: 10.1371/journal.pone.0016075.

Abstract

The assembly of soluble proteins into ordered fibrillar aggregates with cross-β structure is an essential event of many human diseases. The polypeptides undergoing aggregation are generally small in size. To explore if the small size is a primary determinant for the formation of amyloids under pathological conditions we have created two databases of proteins, forming amyloid-related and non-amyloid deposits in human diseases, respectively. The size distributions of the two protein populations are well separated, with the systems forming non-amyloid deposits appearing significantly larger. We have then investigated the propensity of the 486-residue hexokinase-B from Saccharomyces cerevisiae (YHKB) to form amyloid-like fibrils in vitro. This size is intermediate between the size distributions of amyloid and non-amyloid forming proteins. Aggregation was induced under conditions known to be most effective for amyloid formation by normally globular proteins: (i) low pH with salts, (ii) pH 5.5 with trifluoroethanol. In both situations YHKB aggregated very rapidly into species with significant β-sheet structure, as detected using circular dichroism and X-ray diffraction, but a weak Thioflavin T and Congo red binding. Moreover, atomic force microscopy indicated a morphology distinct from typical amyloid fibrils. Both types of aggregates were cytotoxic to human neuroblastoma cells, as indicated by the MTT assay. This analysis indicates that large proteins have a high tendency to form toxic aggregates, but low propensity to form regular amyloid in vivo and that such a behavior is intrinsically determined by the size of the protein, as suggested by the in vitro analysis of our sample protein.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amyloid / biosynthesis*
  • Cell Line, Tumor
  • Hexokinase / chemistry
  • Humans
  • Hydrogen-Ion Concentration
  • Molecular Weight
  • Neuroblastoma / pathology
  • Protein Multimerization
  • Protein Structure, Secondary
  • Proteins / chemistry*
  • Proteins / toxicity
  • Saccharomyces cerevisiae Proteins
  • Solubility

Substances

  • Amyloid
  • Proteins
  • Saccharomyces cerevisiae Proteins
  • Hexokinase