RESUMO
Human recombinant prothymosin alpha (ProTalpha) is known to have coil-like conformation at neutral pH; i.e., it belongs to the class of "natively unfolded" proteins. By means of circular dichroism, SAXS, and ANS fluorescence, we have investigated the effect of several divalent cations on the structure of this protein. Results of these studies are consistent with the conclusion that ProTalpha conformation is unaffected by large excess of Ca(2+), Mg(2+), Mn(2+), Cu(2+), and Ni(2+). However, Zn(2+) induces compaction and considerable rearrangement of the protein structure. This means that ProTalpha can specifically interact with Zn(2+) (K(D) approximately 10(-3) M), and such interactions induce folding of the natively unfolded protein into a compact partially folded (premolten globule-like) conformation. It is possible that these structural changes may be important for the function of this protein.
Assuntos
Precursores de Proteínas/química , Timosina/análogos & derivados , Sequência de Aminoácidos , Sítios de Ligação , Cátions Bivalentes/farmacologia , Dicroísmo Circular , Humanos , Técnicas In Vitro , Cinética , Dados de Sequência Molecular , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/genética , Conformação Proteica/efeitos dos fármacos , Dobramento de Proteína , Precursores de Proteínas/genética , Precursores de Proteínas/metabolismo , Estrutura Secundária de Proteína , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Espalhamento de Radiação , Homologia de Sequência de Aminoácidos , Espectrometria de Fluorescência , Timosina/química , Timosina/genética , Timosina/metabolismo , Zinco/metabolismo , Zinco/farmacologiaRESUMO
Prothymosin alpha has previously been shown to be unfolded at neutral pH, thus belonging to a growing family of "natively unfolded" proteins. The structural properties and conformational stability of recombinant human prothymosin alpha were characterized at neutral and acidic pH by gel filtration, SAXS, circular dichroism, ANS fluorescence, (1)H NMR, and resistance to urea-induced unfolding. Interestingly, prothymosin alpha underwent a cooperative transition from the unfolded state into a partially folded conformation on lowering the pH. This conformation of prothymosin alpha is a compact denatured state, with structural properties different from those of the molten globule. The formation of alpha-helical structure by the glutamic acid-rich elements of the protein accompanied by the partial hydrophobic collapse is expected at lower pH due to the neutralization of the negatively charged residues. It is possible that such conformational changes may be associated with the protein function.
