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University of Zurich, Switzerland
Catching a Glimpse of Sub-Metalated Metallothionein Species
Metallothioneins (MTs) is the name of a superfamily of ubiquitous proteins that are characterized by an extraordinary large cysteine content combined with a small molecular mass (< 10 kDa). Naturally, MTs have a high affinity to thiophilic metal ions and hence function in the homeostasis of ZnII and CuI (depending on the MT sub-form and the producing organism) as well as in the detoxification of CdII, HgII, etc. The efficiency of MTs in these processes is supported by another peculiarity: MTs (mostly) lack secondary structural elements such as a-helices and b-sheets. Hence the (generally) unfolded peptide chain of the metal-free (apo-) MT can wrap around the metal ions very effectively and with very little steric constraints. As a consequence, however, apo-MTs as well as most sub-metalated species are highly flexible impeding their investigation with structural methods. Nevertheless, we succeeded in analyzing the three-dimensional structure of a bacterial MT from Pseudomonas fluorescence and its sub-metalated form with NMR spectroscopy and identified two novel cluster topologies . In addition, the application of potentiometry for the study of a full-length MT is presented for the first time and provides unique insights into histidine coordination in the ZnII– versus the CdII-metalated species.
Project funding by the Swiss National Science Foundation (SNSF) and by the Research Fond (Forschungskredit) of the University of Zurich is gratefully acknowledged.
- Habjanič J., Zerbe O. and Freisinger E., “A histidine-rich Pseudomonas metallothionein with a disordered tail displays higher binding capacity for cadmium than zinc”, Metallomics, Vol. 10, No. 10, (2018), in print.