MASTL
MASTL, also known as Greatwall kinase, is the divergent member of the MAST branch: outside a short kinase-like segment it shares little with MAST1-4 and functions not as a substrate kinase but as a regulator of PP2A-B55. On mitotic activation by CDK1, MASTL phosphorylates the small proteins ENSA and ARPP19, which then bind and inhibit PP2A-B55, permitting accumulation of CDK1-dependent phosphosites that drive mitotic entry, chromosome condensation and progression. MASTL also supports DNA damage recovery and megakaryocyte polyploidisation, and human MASTL variants are associated with thrombocytopenia type 2. Recombinant MASTL is used in mitotic phosphatase-control assays and CDK1-ENSA studies.
