Phosphatase Superfamily CC2

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Phosphatase Classification: Fold CC2: Superfamily CC2

CC2 consists of two member families in human low molecular weight PTP (LWMPTP) and SSU72. Despite having only 15% sequence identity, human LMWPTP and SSU72 structures superimpose with an rmsd of 1.7 Å [1].

A third family, arsenate reductase (ArsC) [2], is only found in prokaryotes. While known to reduce arsenate to arsenite (a similar reaction to the phosphatase reaction), the B. subtilis gene also has in vitro phosphatase activity. A different phosphatase fold, CDC25/Rhodanese also has members in plants and yeast (ACR2) that are capable of arsenate reductase activity, highlighting the similarity of the protein phosphatase and arsenate reductase activities.

Phosphatase domain structure

The CC2 fold/superfamily shares the common CX5R catalytic motif with another two cysteine-based superfamilies, CC1 and CC3.

The two families of CC2 fold/superfamily, LMWPTP and SSU72, share a common fold, a 4-stranded beta sheet sided by helices, in a secondary structure combination of EHEHEHEH in sequence (numbered as E1, H1, E2, E5, H5, E6, H6). The beta strand form the beta sheet with E1, E2, E5, E6.

The two families have some different structure features. The SSU72 family has a 2-stranded beta sheet (formed by E3 and E4) followed by three helices (H2, H3 and H4) between E2 and H5, while the LMWPTP family has two helices (H3-LMWPTP and H4-LMWPTP). The helices of the two families do not align with each other in structure. The SSU72 family also has a helix and a beta strand at C terminus. In other words, The LMWPTP family has a secondary structure combination of E1, H1, E2, H3-LMWPTP, H4-LMWPTP, E5, H5, E6, H6. The SSU72 family has a secondary structure combination of E1, H1, E2, E3, E4, H2, H3, H4, E5, H5, E6, H6, H7, E7.

The LMWPTP family is similar to CC1 fold in the following aspects, while the SSU72 family is more distinct from CC1 fold:

  • The beta sheet. The CC2 fold has a beta sheet formed by E1, E2, E5, E6 (and E7 in SSU72 family); The CC1 fold has a beta sheet formed by E2, E3, E4, E11, E12. The CC2 fold E1, E2, E5 and E6 resemble the CC1 fold E3, E4, E11 and E12, while CC2 E7 and CC1 E2 are at different sides of the beta sheet.
  • CC2 H1 and CC1 H4.
  • The catalytic motif locates between E1 and H1 in CC2 fold, and between E12 and H4 in CC1 fold.


  1. Zhang Y, Zhang M, and Zhang Y. Crystal structure of Ssu72, an essential eukaryotic phosphatase specific for the C-terminal domain of RNA polymerase II, in complex with a transition state analogue. Biochem J. 2011 Mar 15;434(3):435-44. DOI:10.1042/BJ20101471 | PubMed ID:21204787 | HubMed [zhangy11]
  2. Bennett MS, Guan Z, Laurberg M, and Su XD. Bacillus subtilis arsenate reductase is structurally and functionally similar to low molecular weight protein tyrosine phosphatases. Proc Natl Acad Sci U S A. 2001 Nov 20;98(24):13577-82. DOI:10.1073/pnas.241397198 | PubMed ID:11698660 | HubMed [Bennett]
All Medline abstracts: PubMed | HubMed