Figure 6.

Requirement for pyridoxal 5′-phosphate in As/Cd resistance. PLP is a coenzyme for cystathionine β-synthase, which converts serine and homocysteine into cystathionine. Snz1 is essential for PLP synthesis with a putative role as a subunit of PLP synthase, which can explain why our screens revealed that Snz1 is required for cadmium and arsenic tolerance. Consistent with the proposal that Cys11 is a cystathionine β-synthase, we found that it has a predicted PLP attachment site typical of cysteine synthase/cystathionine β-synthase enzymes. Sno1/SPAC222.08c encodes a predicted glutamine aminotransferase which is likely also required for PLP synthesis, thus explaining why Sno1 is required for arsenic resistance and probably also important for cadmium tolerance.