Ca2+ signals:
Molecular Mechanisms and Integrative Functions Collaborative Research Center 894

Project A4 - Richard Zimmermann & Adolfo Cavalié

Mechanisms and regulation of Ca2+ leakage from the ER

Sec61 complexes in the human ER membrane, have been identified and characterized in this project as Ca2+ leak channels that can allow passive Ca2+ efflux from the ER. Furthermore, we identified the ER lumenal chaperone BiP and the cytosolic calmodulin as modulators of the Sec61 dynamics. In our model, BiP inhibits the Ca2+ leakage through Sec61 complexes and calmodulin plays an additional inhibitory role after Ca2+ accumulation in the cytosol. The membrane protein Sec62 and BiP-co-chaperones are involved in the recruitment of BiP and calmodulin to Sec61 complexes.

Next we want to understand the molecular mechanisms of Sec61 channel gating and their contribution to the cellular shift from stress response to apoptosis in further detail and to test our concept at the cellular level as well as in vivo. The role of BiP co-chaperones and other interaction partners of Sec61 complexes will be studied by combining siRNA-mediated gene silencing and live cell Ca2+ imaging. In lipid bilayers, we will analyze the gating kinetics of Sec61 complexes at the single-channel level. Using a multiple myeloma cell model, we will test the hypothesis that a high protein secretion capability makes cells particularly sensitive to Ca2+ leakage from the ER. A therapeutic strategy against SEC62 over-expressing tumors will be evaluated in vivo

Video descriptions:

Putative conformational changes in Sec61 complex gating

(see Dudek et al., 2015 for details)

A) view from the plane of the membrane (by Po-Hsien & Volkhard Helms)

B) view from the cytosol (by Stefan Pfeffer & Friedrich Förster)