Lead is one of the major hazards in human health and its impact on it must be taken into account due to its wide distribution in the environment. The Pb(II) cation preferentially interacts with proteins containing Zn(II) (ALAD, CadC, GATA, Zn-fingers) and Ca(II) (CaM, PKC, syt) causing not only interferences in some metabolic processes (mainly the biosynthesis of hemoglobin) but also the inhibition of several enzymes and damages at the central nervous system (CNS). Living organisms have developed defense and detoxification mechanisms against these deleterious effects of Pb(II), among which we can find metallothioneins (MTs). MTs are among the most versatile metal-binding proteins present in all organisms. Their unusually high Cys content confers them a high capacity to chelate heavy metal ions (e. g. Zn(II), Cd(II), Cu(I), Ag(I), Hg(II), Pb(II)), both in vivo and in vitro, allowing them to act as detoxifying agents. Taking into account this background and the previous studies of our research group, in this PhD Thesis we intended to study the possible role of "The mammalian metallothioneins as detoxifying agents for Pb(II)". To this end, we studied the coordinating ability of the different mammalian MT isoforms, MT1 and MT2 (ubiquitous), MT3 (brain-specific) and MT4 (stratified epithelium) and of yeast, Cup1, tpwards Pb(II). Simultaneously, we analyzed the experimental factors (concentration of MT, T, pH and stabilization time) that may affect such coordination. Spectroscopic (DC, and UV-vis), spectrometric (ESI-TOF MS) and microcalorimetric (ITC) techniques were used. In addition, the Zn or Cu-thionein character of the MTs under study was related to their Pb(II)-binding ability. As a reference, the genuine Cu-tioneína Cup1 from yeast was also studied following the same strategy. Overall, the results show a complex interaction between Pb(II) an each of the mammalian MTs. Therefore, the Pb(II)-binding abilities of a determined mammalian MT isoform cannot be extrapolated from its known Zn- or Cu-thionein character. Turning to specific results, we conclude that MT3 shows the highest Pb(II)-detoxifying capacity under conditions similar to the physiological ones (pH 7. 0, 37 ºC). Furthermore, our results lead us to conclude that, among the experimental factors analyzed here, pH shows the highest influence on the formation and stability of the Pb-MT species. Moreover, it has been demonstrated that the Cu- or Zn-thionein character of MTs does not completely determine the efficiency of the Pb(II) coordination to the protein, but that it influences the way in which the lead coordinates to the protein.
Las metalotioneínas de mamífero como agentes detoxificadores de plomo(II)
Perez Zuñiga, C. T. (Author). 18 Nov 2013
Student thesis: Doctoral thesis
Student thesis: Doctoral thesis