Modularity in Protein Evolution: Modular Organization and De Novo Domain Evolution in Mollusk Metallothioneins

Metallothioneins (MTs) are proteins devoted to the control of metal homeostasis and detoxification, and therefore, MTs have been crucial for the adaptation of the living beings to variable situations of metal bioavailability. The evolution of MTs is, however, not yet fully understood, and to provide new insights into it, we have investigated the MTs in the diverse classes of Mollusks. We have shown that most molluskan MTs are bimodular proteins that combine six domains—α, β1, β2, β3, γ, and δ—in a lineage-specific manner. We have functionally characterized the Neritimorpha β3β1 and the Patellogastropoda γβ1 MTs, demonstrating the metal-binding capacity of the new γ domain. Our results have revealed a modular organization of mollusk MT, whose evolution has been impacted by duplication, loss, and de novo emergence of domains. MTs represent a paradigmatic example of modular evolution probably driven by the structural and functional requirements of metal binding.

Risk for increased metal leakage due to ageing of landfills?

As landfill ages, oxygen will start to penetrate, We investigated whether aeration of a landfillaffected metal leaching, We found that aeration increased cation exchange capacity, butdecreased the buffering capacity and the metal-binding capacity. Leachates from an aeratedlandfill contained less than half the amount of aluminium and iron and more than double theamount of calcium, sulphur and zinc than leachates derived from an identical, but anaerobic,landfill. The leachate from the aerated landfill was capable of extracting metals from theoriginal landfill when recirculated. Leachate from the original landfill treated with leachatefrom the aerated landfill contained more than twice as much cadmium, copper, iron, sulphurand zinc than leachate from the identical anerobic landfill. We conclude that precautionsshould be taken considering the fate of deposited metals when extrapolating results derivedfrom studies on landfills at earlier degradation stages to landfills in more progressed phases.