Prothymosin alpha immunoactive carboxyl-terminal peptide TKKQKTDEDD stimulates lymphocyte reactions, induces dendritic cell maturation and adopts a beta-sheet conformation in a sequence-specific manner

Mol Immunol. 2009 Feb;46(5):784-92. doi: 10.1016/j.molimm.2008.09.014. Epub 2008 Oct 30.


Prothymosin alpha (ProTalpha) is a small acidic polypeptide with important immunostimulatory properties, which we have previously shown to be exerted by its carboxyl (C)-terminus. It exerts immunoenhancing effects through stimulation of monocytes via toll-like receptor (TLR) triggering. Here, we assayed the activity of synthetic peptides homologous to ProTalpha's C-terminus to stimulate lymphocyte functions, in particular natural killer cell cytotoxicity of peripheral blood mononuclear cells isolated from healthy donors. A synthetic decapeptide TKKQKTDEDD was identified as the most potent lymphocyte stimulator. The activity of this peptide was sequence-specific and comparable to that of the intact molecule, suggesting that ProTalpha's immunoactive segment encompasses the nuclear localization signal sequence of the polypeptide. Because ProTalpha stimulates immune responses in a monocyte-dependent manner, we further investigated whether the entire molecule and its peptide TKKQKTDEDD specifically act on monocytes and show that both can promote maturation of monocyte-derived dendritic cells (DC). Finally, knowing that, under specific conditions, ProTalpha forms amyloid fibrils, we studied the amyloidogenic properties of its C-terminal peptide segments, utilizing ATR FT-IR spectroscopy and transmission electron microscopy (negative staining). Although the peptide TKKQKTDEDD adopts an antiparallel beta-sheet conformation under various conditions, it does not form amyloid fibrils; rather it aggregates in globular particles. These data, in conjunction with reports showing that the peptide TKKQKTDEDD is generated in vivo upon caspase-cleavage of ProTalpha during apoptosis, strengthen our hypothesis that immune response stimulation by ProTalpha is in principle exerted via its bioactive C-terminal decapaptide, which can acquire a sequence-specific beta-sheet conformation and induce DC maturation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amyloid / immunology
  • Apoptosis / drug effects
  • Apoptosis / immunology
  • Caspases / immunology
  • Cells, Cultured
  • Dendritic Cells / cytology
  • Dendritic Cells / immunology*
  • Humans
  • Lymphocytes / cytology
  • Lymphocytes / immunology*
  • Monocytes / cytology
  • Monocytes / immunology*
  • Peptides / chemistry
  • Peptides / immunology
  • Peptides / pharmacology*
  • Protein Precursors / chemistry
  • Protein Precursors / immunology
  • Protein Precursors / pharmacology*
  • Protein Structure, Secondary / physiology
  • Thymosin / analogs & derivatives*
  • Thymosin / chemistry
  • Thymosin / immunology
  • Thymosin / pharmacology
  • Toll-Like Receptors / immunology


  • Amyloid
  • Peptides
  • Protein Precursors
  • Toll-Like Receptors
  • prothymosin alpha
  • Thymosin
  • Caspases