The eukaryotic host factor that activates exoenzyme S of Pseudomonas aeruginosa is a member of the 14-3-3 protein family

Cloning and characterization of the epsilon and zeta isoforms of the 14-3-3 proteins

Two prominent proteins (30 and 33 kD) in a purified preparation of the sheep pineal gland were studied. Amino acid analysis of tryptic peptides indicated that the 33-kD protein was the epsilon isoform of the 14-3-3 family of proteins, and that the 30-kD protein was the zeta isoform. The sheep pineal gland was found to have six other 14-3-3 isoforms in addition to the epsilon and zeta, suggesting that copurification of the epsilon and zeta forms may reflect the existence of homo- or heterodimers comprised of these isoforms. To characterize 14-3-3 proteins further in the pineal gland, the full sequence of the epsilon isoform and a partial sequence of the zeta isoform were cloned from a rat pineal cDNA library and are reported here. Tissue distribution studies using Western blot analysis revealed that rat pineal and retina have levels of 14-3-3 protein similar to those found in brain, and that relatively low levels occur in other tissues. This investigation also revealed the epsilon isoform was present at high levels in the rat pineal gland early in development and decreased steadily thereafter and that 30-kD isoforms exhibited the inverse developmental pattern.

Mechanism of inhibition of protein kinase C by 14-3-3 isoforms. 14-3-3 isoforms do not have phospholipase A2 activity

The ability of individual members of the 14-3-3 protein family to inhibit protein kinase C (PKC) has been studied by using a synthetic peptide based on the specific 80 kDa substrate for PKC (MARCKS protein) in two different assay systems. Recombinant 14-3-3 and isoforms renatured by a novel method after separation by reverse-phase h.p.l.c. were studied. The detailed effects of diacylglycerol and the phorbol ester phorbol 12-myristate 13-acetate on the inhibition were also investigated. This suggests that one of the sites of interaction of 14-3-3 may be the cysteine-rich (C1) domain in PKC. Since a region in secreted phospholipase A2 (PLA2) shares similarity with this domain, the ability of 14-3-3 to interact with mammalian PLA2 was studied. Cytosolic PLA2 has some similarity to the C2 region of PKC, and the effect of 14-3-3 on this class of PLA2 was also analysed. In contrast with a previous report, no PLA2 activity was found in brain 14-3-3, nor in any of the recombinant proteins tested. These include zeta 14-3-3 isoform, on which the original observation was made.

Antibodies against the major brain isoforms of 14-3-3 protein. An antibody specific for the N-acetylated amino-terminus of a protein

14-3-3 proteins are apparently ubiquitous eukaryotic proteins that comprise a large number of isoforms. They have been implicated in the regulation of a wide range of biological processes [reviewed in Aitken et al. (1992) Trends Biochem. Sci. 17, 498-501]. We have raised specific antibodies against each mammalian brain isoform of 14-3-3 employing peptides synthesised from the amino-terminal regions. The peptides were, like the proteins from mammalian brain, N-acetylated. The antiserum specific for the epsilon isoform did not recognise the recombinant form of this protein (lacking the N-acetyl co-translational modification) expressed in E. coli until it was chemically acetylated.