3bsqA Discussion

Multiple sequence alighment (MSA) revealed some conserved residues throughput the whole sulfatase family. Previous experiemnts on catalytic activity of sulfatases describe a set of residues which are essential for the function of sulfatases. A histidine residue (H) and two or more sequential arganine residues (R) are known to be essential, and also characteristic of the N-terminal active site of sulfatases. Our MSA resultaed a number of residues conserves in the N-terminus, along with a H and one R residue. When these conserved residues were marked in the three dimenetional view of ASK in PyMol, they all seemed clustered within a certain region of the molecule. This region is found in the core of the molecule, directly inside a pocket-like surface feature. This region is assumed to be the 'possible active site' of the protein.

Previous investigation has revealed that arylsulfatases D,E,F,G,H,J snd K are localysed in ER and golgi compartments of the cell ([[1]] Ghosh, D., 2007). Human Steroid sulfatase (STS) which has similar sequence fratures to ASK is also localysed in ER. However STS is a membrane bound protein which consists of a globular domain bearing the catalytic site and a transmembrane domain made up of two antiparallel hydrophobic alpha helices. Structural features of ASK do not show an transmembrane domain, therfore it has to be a metrix soluble enzyme(Ghosh, D., 2007).

Studies on the catalytic site of sulfatases, characterised by STS, ASA and ASB, has shown that catalytic site is compsoed with a set of very highly conserved residues, which include Asp, Cys, Arg, Lys and His. the site is also observed deep inside the molecule connected to exterior by a hydrophobic substrate entry path(Ghosh, D., 2007).

Results of structural comparisons and protein-protein interactions resulted several other proteins, which were used for a second multiple sequence alighment. This alighment also showed a certain degree of conservation of previously described conserved residues.