Poster: Membrane transport

Abs # 175: Regulation of calcium transporters: The role of a nuclear-localized CAX-interacting protein, CXIP4

Presenter:	Cheng, Ning-Hui , ncheng@bcm.tmc.edu
Authors	Cheng, Ning-Hui  (A)   Rees, Ian  (A)
Affiliations:	(A): Baylor College of Medicine

Regulation of calcium transporters is essential for modulating the Ca²⁺ signaling and/or Ca²⁺ homeostasis that are involved in the growth and adaptation of all organisms. The Arabidopsis H⁺ /Ca²⁺ antiporters, CAX1 and CAX1-like transporters, are autoinhibited and unable to suppress the hypersensitivity of yeast vacuolar Ca²⁺ transporter mutants when heterologously expressed in yeast cell. Using a yeast functional screen, we identified several CAX interacting proteins (1-5) that activated full-length CAX1, but not full-length CAX2, CAX3 or CAX4. One of these, CXIP4, encodes a novel plant protein with no bacterial, fungal, animal and mammalian homologs. CXIP4 is highly expressed in all tissues of Arabidopsis. Expression of full-length CXIP4-GFP fusion in yeast and plant cells suggests that CXIP4 is predominately targeted to the nucleus. Using a yeast growth assay, we also demonstrated that CXIP4 activated a chimeric CAX construct that contained specific portions of the N-terminus of CAX1. CXIP4 has a unique structural feather, such as a Zn knuckle (CX2CX4HX4C motif) at the N-terminus and the multiple putative nuclear localized signal (NLS) motifs at its C-terminal region. Further investigation of the role of CXIP4 in regulating CAX-mediated Ca²⁺ transport will be presented in the meeting. A potential link between nuclear-localized signal molecule and Ca²⁺ signaling will also be discussed.