Propriedades termodinâmicas da Prolil Oligopeptidase de Trypanosoma brucei

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Trypanosoma brucei secrets a prolyl oligopeptidase (POPTb) which is possibly involved in the pathogenesis of sleeping sickness. It is able to hydrolyze prolinecontaining peptide hormones and is therefore considered a good target for the development of drugs to treat the disease. As the crystal structure of POPTb has not been solved yet, we used circular dichroism and fluorescence spectroscopy to gain some knowledge on the enzyme structure, stability and on additive effects for both crystallization assays and storage. Thermodynamic and structural parameters were calculated from thermal and chemical denaturation studies as well as from fluorescence quenching experiments, respectively. The concentration of guanidine hydrochloride (GuHCl) that led to protein denaturation was nearly 30% that of urea needed to reach the same effect. Divergence in the ΔG values derived from chemical and thermal unfolding assays suggests the presence of intermediate states in the process. It also suggests higher structural stability. Sorbitol increases enzyme stability and 0.1 mM cetyl trimethyl ammonium bromide (CTAB) decreases it almost halting enzyme activity. Ditiotreitol (DTT), however, has the former effect in alkaline pH and the latter effect in neutral pH. Fluorescence quenching experiments show dependence on pH and indicate heterogeneity in the environment of the surface-accessible tryptophan residues with at least one such residue near the enzyme active site. POPTb molecule seems to be less subjected to conformational changes at pH 7.5. The increase in temperature lowers CTAB critical micelle concentration (cmc).

ASSUNTO(S)

trypanosoma brucei estabilidade prolil oligopeptidase desnaturação química medicina desnaturação térmica

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