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.
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.
Skopeliti
Margarita
M
Department of Animal and Human Physiology, Faculty of Biology, University of Athens, Athens, Greece. mskopelit@biol.uoa.gr
Iconomidou
Vassiliki A
VA
Derhovanessian
Evelyna
E
Pawelec
Graham
G
Voelter
Wolfgang
W
Kalbacher
Hubert
H
Hamodrakas
Stavros J
SJ
Tsitsilonis
Ourania E
OE
D000682:Amyloid / Q000276:immunology; D017209:Apoptosis / Q000187:drug effects / Q000276:immunology; D020169:Caspases / Q000276:immunology; D002478:Cells, Cultured; D003713:Dendritic Cells / Q000166:cytology / Q000276:immunology*; D006801:Humans; D008214:Lymphocytes / Q000166:cytology / Q000276:immunology*; D009000:Monocytes / Q000166:cytology / Q000276:immunology*; D010455:Peptides / Q000737:chemistry / Q000276:immunology / Q000494:pharmacology*; D011498:Protein Precursors / Q000737:chemistry / Q000276:immunology / Q000494:pharmacology*; D017433:Protein Structure, Secondary / Q000502:physiology; D013947:Thymosin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000276:immunology / Q000494:pharmacology; D051193:Toll-Like Receptors / Q000276:immunology
D000682:Amyloid; D010455:Peptides; D011498:Protein Precursors; D051193:Toll-Like Receptors; C040782:prothymosin alpha; D013947:Thymosin; D020169:Caspases