Functional role of the flexible N-terminal extension of FKBP38 in catalysis.

Congbao Kang, Hong Ye, Joel Chia, Bo-Hwa Choi, Sirano Dhe-Paganon, Bernd Simon, Ulrike Schütz, Michael Sattler, Ho Sup Yoon

Index: Sci. Rep. 3 , 2985, (2013)

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Abstract

FKBP38 regulates apoptosis through unique interactions with multiple regulators including Bcl-2. Interestingly, the peptidylprolyl isomerase activity of FKBP38 is only detectable when it binds to calcium-saturated calmodulin (CaM/Ca(2+)). This, in turn, permits the formation of a complex with Bcl-2. FKBP38 thereby provides an important link between isomerase activity and apoptotic pathways. Here, we show that the N-terminal extension (residues 1-32) preceding the catalytic domain of FKBP38 has an autoinhibitory activity. The core isomerase activity of FKBP38 is inhibited by transient interactions involving the flexible N-terminal extension that precedes the catalytic domain. Notably, CaM/Ca(2+) binds to this N-terminal extension and thereby releases the autoinhibitory contacts between the N-terminal extension and the catalytic domain, thus potentiating the isomerase activity of FKBP38. Our data demonstrate how CaM/Ca(2+) modulates the catalytic activity of FKBP38.