#phosphatase

Cell Cycle Regulation

Which enzyme removes inhibitory phosphate from CDK1 to activate mitosis?

Release from Wee1-mediated inhibition is pivotal for mitotic entry, executed by Cdc25 family of dual specificity phosphatases capable of hydrolyzing phospho-threonine, phospho-serine and phospho-tyrosine. Three isoforms A, B, C exist in mammals, each with N-terminal regulatory domain containing 14-3-3 binding sites, nuclear export signals, Polo box binding motifs, and C-terminal catalytic domain bearing HCX5R active site with catalytic cysteine. During unperturbed cycle Cdc25B initiates activation at centrosomes early G2, followed by Cdc25C amplifying response. Polo-like kinase 1 phosphorylate

Ref: Nilsson & Hoffmann, Cdc25 Phosphatases Activate CDK1 for Mitosis, Cell Cycle 2000; Alberts et al., Chapter 17, Cdc25 Function.

View Details

Cell Cycle Regulation

Which phosphatase deactivates mitotic CDKs to promote exit from mitosis?

Lowering mitotic kinase activity requires collaboration between ubiquitin mediated cyclin destruction and phosphatase mediated substrate dephosphorylation. APC/C-Cdc20 degrades cyclin B reducing CDK1 catalytic availability, but hundreds of phosphorylated residues remain. Phosphatases execute erasure. In yeast, Cdc14 is dominant enzyme preferentially dephosphorylating proline-directed CDK sites, including Cdh1 to activate APC/C-Cdh1 for further cyclin clearance, Swi5 for Sic1 transcription and structural cytokinesis proteins. In metazoa, PP2A-B55 family is major mitotic exit phosphatase regulat

Ref: Wurzenberger & Gerlich, Mitotic Phosphatases PP2A and Cdc14 in Exit, J Cell Biol 2011; NCBI Bookshelf, Regulation of Mitotic Exit.

View Details

Cell Signaling ELR Pathways - I

Which phosphatase antagonizes PI3K signaling?

PTEN, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

View Details

Cell Signaling GPCR Pathways - I

In feedback circuits, phosphatase mainly functions to

remove phosphate, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

View Details