A Bacterial Alkaline Phosphodiesterase with the structure of a Purple Acid Phosphatase

LILLINGTON JAMES E.D. ; RODRIGUEZ FERNANDA; JOHNSON STEVEN ; ROVERSI PIETRO ; BEN BERKS; LEA SUSAN M.

Reading

Encuentro; BCA meeting; 2010

PhoD of Bacillius subtilis is only expressed under phosphate starvation conditions in order to free up phosphates for nutrition. The structure of this purple coloured alkaline phosphodiesterase has been solved to 1.9 Å. The catalytic site is similar to the conserved site of the eukaryotic purple acid phosphatases (PAPs), containing an invariant Fe(III) and variant M(II) - in this case a Zn(II). As with the PAPs, the colour derives from an Fe(III) - tyrosine charge transfer band, however there are differences to other PAP Fe(III) coordination ligands. Highly unusually, in this hexagonal coordination of Fe(III) there is a single cysteine residue – a pairing only before seen in desulfoferrodoxin/neelaredoxin type environments and clusters. Another interesting feature of the catalytic site is its apparent occlusion by a capping helix in the crystal structure. Current work is underway to understand whether this is a selectivity or processivity feature of the phosphodiesterase.