BCR kinase phosphorylates 14-3-3 Tau on residue 233.

The breakpoint cluster region protein, BCR, has protein kinase activity that can auto- and trans-phosphorylate serine, threonine and tyrosine residues. BCR has been implicated in chronic myelogenous leukaemia as well as important signalling pathways, and as such its interaction with 14-3-3 is of major interest. 14-3-3tau and zeta isoforms have been shown previously to be phosphorylated in vitro and in vivo by BCR kinase on serine and threonine residue(s) but site(s) were not determined. Phosphorylation of 14-3-3 isoforms at distinct sites is an important mode of regulation that negatively affects interaction with Raf kinase and Bax, and potentially influences the dimerization of 14-3-3. In this study we have further characterized the BCR-14-3-3 interaction and have identified the site phosphorylated by BCR. We show here that BCR interacts with at least five isoforms of 14-3-3 in vivo and phosphorylates 14-3-3tau on Ser233 and to a lesser extent 14-3-3zeta on Thr233. We have previously shown that these two isoforms are also phosphorylated at this site by casein kinase 1, which, in contrast to BCR, preferentially phosphorylates 14-3-3zeta.

A nonphosphorylated 14-3-3 binding motif on exoenzyme S that is functional in vivo.

14-3-3 proteins play an important role in a multitude of signalling pathways. The interactions between 14-3-3 and other signalling proteins, such as Raf and KSR (kinase suppressor of Ras), occur in a phospho-specific manner. Recently, a phosphorylation-independent interaction has been reported to occur between 14-3-3 and several proteins, for example 5-phosphatase, p75NTR-associated cell death executor (NADE) and the bacterial toxin Exoenzyme S (ExoS), an ADP-ribosyltransferase from Pseudomonas aeruginosa. In this study we have identified the amino acid residues on ExoS, which are responsible for its specific interaction with 14-3-3. Furthermore, we show that a peptide derived from ExoS, containing the 14-3-3 interaction site, effectively competes out the interaction between ExoS and 14-3-3. In addition, competition with this peptide blocks ExoS modification of Ras in our Ras modification assay. We show that the ExoS protein interacts with all isoforms of the 14-3-3 family tested. Moreover, in vivo an ExoS protein lacking the 14-3-3 binding site has a reduced capacity to ADP ribosylate cytoplasmic proteins, e.g. Ras, and shows a reduced capacity to change the morphology of infected cells.

TAPAS-1, a novel microdomain within the unique N-terminal region of the PDE4A1 cAMP-specific phosphodiesterase that allows rapid, Ca2+-triggered membrane association with selectivity for interaction with phosphatidic acid.

Here we identify an 11-residue helical module in the unique N-terminal region of the cyclic AMP-specific phosphodiesterase PDE4A1 that determines association with phospholipid bilayers and shows a profound selectivity for interaction with phosphatidic acid (PA). This module contains a core bilayer insertion unit that is formed by two tryptophan residues, Trp(19) and Trp(20), whose orientation is optimized for bilayer insertion by the Leu(16):Val(17) pairing. Ca(2+), at submicromolar levels, interacts with Asp(21) in this module and serves to gate bilayer insertion, which is completed within 10 ms. Selectivity for interaction with PA is suggested to be achieved primarily through the formation of a charge network of the form (Asp(21-):Ca(2+):PA(2-):Lys(24+)) with overall neutrality at the bilayer surface. This novel phospholipid-binding domain, which we call TAPAS-1 (tryptophan anchoring phosphatidic acid selective-binding domain 1), is here identified as being responsible for membrane association of the PDE4A1 cAMP-specific phosphodiesterase. TAPAS-1 may not only serve as a paradigm for other PA-binding domains but also aid in detecting related phospholipid-binding domains and in generating simple chimeras for conferring membrane association and intracellular targeting on defined proteins.