ABSTRACT
Arsenic is a toxic metalloid that is widespread in the environment from geochemical and anthropogenic sources. In bacteria, the principal arsenic detoxification mechanism is based on reduction of intracellular arsenate to arsenite by cytoplasmic arsenate reductases (ArsCs). Arsenite is pumped out of the cell by specific arsenite efflux permeases. ArsCs are small cytoplasmic redox enzymes intensely studied during the last two decades (Messens & Silver 2006; Mukhopadhyay & Rosen 2002). For reduction, ArsC makes use of electrons coming from the cellular redox system. Electrons are transferred from NADPH by the sequential involvement of three different thiolate nucleophiles, but different mechanisms arose independently during evolution. Based on different reduction mechanisms and structural folds, several distinct ArsC classes can be defined (Messens & Silver 2006; Mukhopadhyay & Rosen 2002). We recently found in C. glutamicum that the arsenate reductases Cg_ArsC1 and Cg_ArsC2 belongs to a new class: the mycothiol (MSH)/mycoredoxin (Mrx) dependent class (Ordóñez et al., 2009). These are also the first identified enzymes that use MSH and Mrx in a thol/disulfide redox cascade.
