Poster: Intracellular Signaling

Abs # 847: Ion Binding Activity of Dehydrins is Dependent on Phosphorylation

Presenter:	Alsheikh, Muath , malsheik@iupui.edu
Authors	Alsheikh, Muath  (A)   Svensson, Jan  (B)   Randall, Stephen  (A)
Affiliations:	(A): Indiana University-Purdue University Indianapolis (B): University of California at Riverside

Cold and drought are major limitations to agricultural productivity. One of the early responses of some plants to these environmental stresses is an increase in levels of a group of proteins termed dehydrins. Little is known about biochemical function and physiological role of these proteins in plants. Dehydrins are characterised by the presence of at least one K-domain, a Lys-rich sequence, and many contain the S-domain, a Ser-rich sequence. Here, we demonstrate a biochemical function of several known dehydrins. We purified five recombinant Arabidopsis dehydrins (ERD10, ERD14, COR47, RAB18, and XERO2) by ion exchange chromatography. When phosphorylated (with casein kinase II), ERD10, ERD14, COR47, and RAB18 showed a shift in apparent mass on SDS-PAGE gel. ERD14 exhibited the highest calcium-binding activity followed by ERD10 and COR47. RAB18 showed very little calcium binding activity (less than 2% of ERD14). XERO2 was not phosphorylated with CKII and also did not bind calcium. Calcium-binding properties of ERD14 derived from Arabidopsis extracts were comparable to E. coli expressed ERD14. Based on the stoichiometry of CKII-phosphorylated ERD14, phosphorylation occurs at a minimum of two phosphorylation sites. Further analyses suggested that threonine and serine are possible phosphorylation sites on ERD14. Utilizing MALDI-TOF, we have identified three phosphorylated peptides in both in vivo and in vitro phosphorylated ERD14. We believe the most likely candidate responsible for the gel-shifting and calcium-binding activation to be the poly-serine domain. This site is perfectly conserved in ERD10, COR47, and RAB18. We are presently determining the exact phosphorylation sites on in vitro and in vivo ERD10, COR47 and RAB18 that are responsible for calcium-binding activity.