Phosphatase Superfamily Rhodanese
Phosphatase Classification: Fold CC3 (Rhodanese): Superfamily CC3 (Rhodanese)
Phosphatase superfamily Cys-based II has a catalytic phosphatase domain of rhondanese fold. The catalytic domain shares the common Cys-based catalytic motif Cx5R with another two superfamilies CC1 and CC3, but it has distinct fold from them. Although the superfamily consists of at least families in SCOP database (here and here), only CDC25 family has protein phosphatase activitiy.
Not all rhodanese domains have phosphatase activity
Rhodanese domains are ubiquitous structural domains found in both eukaryotes and prokaryotes. It is named after bovine liver rhodanese, the most well characterized sufurtranferase. The fold and its single superfamily consists of at least ten families based on different domain combination [1]. The member proteins have various functions and physiological substrates, such as, thiosulfate:cyanide sulfurtransferase, protein phosphatase, and arsenate reductase. The cysteine at catalytic site is necessary for its activity no matter what its substrate is. But, whether the functional specificity is determined solely by catalytic motif is unknown, though it seems different families have different catalytic motif in length and conserved residues [1].
The rhodanese domain occurs not only in this superfamily but also in some dual-specificity phosphatases (DSPs) of CC1 superfamily. However, the cysteine at catalytic site is replaced by aspartic acid or glutamic acid in these DSPs, which results in inactive rhodanese domain rather than two active phosphatase domains within the same protein.
