22541-54-4Relevant articles and documents
Kinetic analysis of arsenic-metalation of human metallothionein: Significance of the two-domain structure
Ngu, Thanh T.,Easton, Alexandria,Stillman, Martin J.
, p. 17016 - 17028 (2008)
Metallothionein (MT) is ubiquitous in Nature, underlying MT's importance in the cellular chemistry of metals. Mammalian MT consists of two metal-binding domains while microorganisms like cyanobacteria consist of a single metal-binding domain MT. The evolution of a two-domain protein has been speculated on for some time; however, no conclusive evidence explaining the evolutionary necessity of the two-domain structure has been reported. The results presented in this report provide the complete kinetic analysis and subsequent mechanism of the As3+-metalation of the two-domain βαhMT and the isolated single domain fragments using time- and temperature-resolved electrospray ionization mass spectrometry. The mechanism for βαhMT binding As3+ is noncooperative and involves six sequential bimolecular reactions in which the ∞ domain binds As 3+ first followed by the β domain. At room temperature (295 K) and pH 3.5, the sequential individual rate constants, kn (n = 1-6) for the As3+-metalation of βαhMT starting at k 1βα are 25, 24, 19, 14, 8.7, and 3.7 M-1s -1. The six rate constants follow an almost linear trend directly dependent on the number of unoccupied sites for the incoming metal. Analysis of the temperature-dependent kinetic electrospray ionization mass spectra data allowed determination of the activation energy for the formation of As 1-H17-βαhMT (14 kJ mol-1) and As2-6-βαhMT (22 kJ mol-1). On the basis of the increased rate of metalation for the two-domain protein when compared with the isolated single-domain, we propose that there is an evolutionary advantage for the two-domain MT structures in higher organism, which allows MT to bind metals faster and, therefore, be a more efficient metal scavenger.
