This is a EF-hand domain found in Serine/threonine-protein phosphatase 2A regulatory subunit B'' subunit beta (P2R3B) [1,2]. This protein may modulate substrate selectivity and catalytic activity.

1: Structure of the Ca2+-dependent PP2A heterotrimer and insights into Cdc6 dephosphorylation. Wlodarchak N, Guo F, Satyshur KA, Jiang L, Jeffrey PD, Sun T, Stanevich V, Mumby MC, Xing Y; Cell Res. 2013;23:931-946. PMID:23752926

2: Structural and biochemical characterization of human PR70 in isolation and in complex with the scaffolding subunit of protein phosphatase 2A. Dovega R, Tsutakawa S, Quistgaard EM, Anandapadamanaban M, Low C, Nordlund P; PLoS One. 2014;9:e101846. PMID:25007185