Structural and functional studies on molecular evolution of calcium signaling tool kit

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One of the fundamental and challenging questions in the calcium biology field is how far the calcium signaling mechanisms and legacy go back in the evolution of unicellular and multicellular organisms? In previous years, we identified an inositol 1,4,5-trisphosphate receptor (IP3R) homologue from a parasitic protist, Trypanosoma cruzi and demonstrated that T. cruzi IP3R (TcIP3R) is a novel virulence factor regulating replication, differentiation and infectivity of T. cruzi. Our future studies focus on key members of the calcium signaling toolkit, including those from a primitive multicellular organism, C. elegans. In this proposal we will study the primitive homologues of human stromal interacting proteins (STIMs) and ORAI Ca2+ channels, which were recently shown to play a crucial role in the store-operated calcium entry (SOCE) function in various cell types in mammals. Two isoforms of STIMs (STIM1 and STIM2) function as endoplasmic reticulum (ER) luminal Ca2+ sensors and activate ORAI Ca2+ channels, which have three isoforms (ORAI1, 2 lcium signals have been utilized for physiological functions of various organisms. Our recent structural studies on C.elegans STIM (ceSTIM) have shown that the N-terminal domain, which is exposed to the ER lumen, possesses a previously unidentified kinked helix at the N-terminus, which may explain the constitutive localization at the cell periphery in puncta under basal ER Ca2+ levels that is specific to ceSTIMs. We have also been studying C. elegans ORAI (ceORAI) as well as human ORAI isoforms and succeeded in expression and purification of the multimeric functional form of the ceORAI channel. We plan to perform further structural and functional studies on ceSTIM and ceORAI in order to elucidate common and diverged mechanisms associated with SOCE between C. elegans and mammals. We believe that our studies of ancestral IP3R, STIM and ORAI homologues will provide important clues to understanding the isoform-specific roles of the individual isoforms in humans and other mammals, which roles have been inherited from simpler organisms to humans as essential biological functions, and which roles have evolved in higher organisms to adapt to more complicated survival strategies. *****