Molecular cloning,expression, overproduction and characterization of human TRAIP Leucine zipper protein

The TRAIP interacting protein is known as a negative regulator of TNF-induced-nuclear factor, kappa-light-chain-enhancer of activated B cell (NF-κB) by direct interaction with the adaptor protein TRAF2, which inhibits the function of TRAF2 via the RINGCC domain protein. The TRAIP protein is composed of 469 amino acids with an N-terminal RING motif that is followed by a coiled coil (CC) and leucine zipper domain. TRAIP proteins are critical in programmed cell death, cell proliferation and differentiation, and embryonic development. The critical functions of TRAIP together with the molecular inhibitory mechanism effect of TRAIP have been reported by two different studies and have opened up new research into the field of TRAF biology. In this study, we designed different constructs of the Leucine zipper domain to find the over –expressed construct for further studies. We successfully cloned the C-terminal TRAIP containing the leucine zipper domain. In addition, we have over-expressed and purified the TRAIP LZ for their biochemical characterization.     

Glucocorticoid-induced leucine zipper (GILZ) mediates glucocorticoid action and inhibits inflammatory cytokine-induced COX-2 expression

Cyclooxygenase-2 (COX-2) plays an important role in rheumatoid arthritis and therefore, has been a major target for anti-arthritis therapies. The expression of COX-2 is induced by inflammatory cytokines such as TNF-alpha and IL-1beta, and inhibited by glucocorticoids. However, the molecular mechanisms underlying the anti-inflammatory and immune suppressive actions of glucocorticoids are not well defined. Here we report that glucocorticoid-induced leucine zipper (GILZ) mimics glucocorticoid action and inhibits inflammatory cytokine-induced COX-2 expression in bone marrow mesenchymal stem cells, the cells that have been recently implicated in the pathogenesis and progression of rheumatoid arthritis. Using a retrovirus-mediated gene expression approach we demonstrate that overexpression of GILZ inhibits TNF-alpha and IL-1beta-induced COX-2 mRNA and protein expression, and knockdown of GILZ by shRNA reduces glucocorticoid inhibition of cytokine-induced COX-2 expression. Consistent to these results, overexpression of GILZ also inhibits NF-kappaB-mediated COX-2 promoter activity. Finally, we show that GILZ inhibits COX-2 expression by blocking NF-kappaB nuclear translocation. Our results suggest that GILZ is a key glucocorticoid effect mediator and that GILZ may have therapeutic value for novel anti-inflammation therapies.     

Probing the interaction between the coiled coil leucine zipper of cGMP-dependent protein kinase Ialpha and the C terminus of the myosin binding subunit of the myosin light chain phosphatase

Nitric oxide and nitrovasodilators induce vascular smooth muscle cell relaxation in part by cGMP-dependent protein kinase I (PKG-Ialpha)-mediated activation of myosin phosphatase (MLCP). Mechanistically it has been proposed that protein-protein interactions between the N-terminal leucine zipper (LZ) domain of PKG-Ialpha ((PKG-Ialpha(1-59)) and the LZ and/or coiled coil (CC) domain of the myosin binding subunit (MBS) of MLCP are localized in the C terminus of MBS. Although recent studies have supported these interactions, the critical amino acids responsible for these interactions have not been identified. Here we present structural and biophysical data identifying that the LZ domain of PKG-Ialpha(1-59) interacts with a well defined 42-residue CC motif (MBS(CT42)) within the C terminus of MBS. Using glutathione S-transferase pulldown experiments, chemical cross-linking, size exclusion chromatography, circular dichroism, and isothermal titration calorimetry we identified a weak dimer-dimer interaction between PKG-Ialpha(1-59) and this C-terminal CC domain of MBS. The K(d) of this non-covalent complex is 178.0+/-1.5 microm. Furthermore our (1)H-(15)N heteronuclear single quantum correlation NMR data illustrate that this interaction is mediated by several PKG-Ialpha residues that are on the a, d, e, and g hydrophobic and electrostatic interface of the C-terminal heptad layers 2, 4, and 5 of PKG-Ialpha. Taken together these data support a role for the LZ domain of PKG-Ialpha and the CC domain of MBS in this requisite contractile complex.     

The trimerization domain of NEMO is composed of the interacting C-terminal CC2 and LZ coiled-coil subdomains

NEMO (NF-kappaB essential modulator) plays a key role in the canonical NF-kappaB pathway as the scaffold/regulatory component of the IkappaB kinase (IKK) complex. The self-association of NEMO involves the C-terminal halves of the polypeptide chains containing two putative coiled-coil motifs (a CC2 and a LZ leucine zipper), a proline-rich region, and a ZF zinc finger motif. Using purified truncation mutants, we showed that the minimal oligomerization domain of NEMO is the CC2-LZ segment and that both CC2 and LZ subdomains are necessary to restore the LPS-dependent activation of the NF-kappaB pathway in a NEMO-deficient cell line. We confirmed the association of the oligomerization domain in a trimer and investigated the specific role of CC2 and LZ subdomains in the building of the oligomer. Whereas a recombinant CC2-LZ polypeptide self-associated into a trimer with an association constant close to that of the wild-type protein, the isolated CC2 and LZ peptides, respectively, formed trimers and dimers with weaker association constants. Upon mixing, isolated CC2 and LZ peptides associated to form a stable hetero-hexamer as shown by gel filtration and fluorescence anisotropy experiments. We propose a structural model for the organization of the oligomerization domain of activated NEMO in which three C-terminal domains associate into a pseudo-hexamer forming a six-helix bundle. This model is discussed in relation to the mechanism of activation of the IKK complex by upstream activators.     

A novel leucine zipper targets AKAP15 and cyclic AMP-dependent protein kinase to the C terminus of the skeletal muscle Ca2+ channel and modulates its function.

In skeletal muscle, voltage-dependent potentiation of L-type Ca(2+) channel (Ca(V)1.1) activity requires phosphorylation by cyclic AMP-dependent protein kinase (PKA) anchored via an A kinase-anchoring protein (AKAP15). However, the mechanism by which AKAP15 targets PKA to L-type Ca(2+) channels has not been elucidated. Here we report that AKAP15 directly interacts with the C-terminal domain of the alpha(1) subunit of Ca(V)1.1 via a leucine zipper (LZ) motif. Disruption of the LZ interaction effectively inhibits voltage-dependent potentiation of L-type Ca(2+) channels in skeletal muscle cells. Our results reveal a novel mechanism whereby anchoring of PKA to Ca(2+) channels via LZ interactions ensures rapid and efficient phosphorylation of Ca(2+) channels in response to local signals such as cAMP and depolarization.     

Mechanism of DNA binding by the DnaB helicase of Escherichia coli: analysis of the roles of domain gamma in DNA binding.

We have analyzed the mechanism of single-stranded DNA (ssDNA) binding mediated by the C-terminal domain gamma of the DnaB helicase of Escherichia coli. Sequence analysis of this domain indicated a specific basic region, "RSRARR", and a leucine zipper motif that are likely involved in ssDNA binding. We have carried out deletion as well as in vitro mutagenesis of specific amino acid residues in this region in order to determine their function(s) in DNA binding. The functions of the RSRARR domain in DNA binding were analyzed by site-directed mutagenesis. DnaBMut1, with mutations R(328)A and R(329)A, had a significant decrease in the DNA dependence of ATPase activity and lost its DNA helicase activity completely, indicating the important roles of these residues in DNA binding and helicase activities. DnaBMut2, with mutations R(324)A and R(326)A, had significantly attenuated DNA binding as well as DNA-dependent ATPase and DNA helicase activities, indicating that these residues also play a role in DNA binding and helicase activities. The role(s) of the leucine zipper dimerization motif was (were) determined by deletion analysis. The DnaB Delta 1 mutant with a 55 amino acid C-terminal deletion, which left the leucine zipper and basic DNA binding regions intact, retained DNA binding as well as DNA helicase activities. However, the DnaB Delta 2 mutant with a 113 amino acid C-terminal deletion that included the leucine zipper dimerization motif, but not the RSRARR sequence, lost DNA binding, DNA helicase activities, and hexamer formation. The major findings of this study are (i) the leucine zipper dimerization domain, I(361)-L(389), is absolutely required for (a) dimerization and (b) ssDNA binding; (ii) the base-rich RSRARR sequence is required for DNA binding; (iii) three regions of domain gamma (gamma I, gamma II, and gamma III) differentially regulate the ATPase activity; (iv) there are likely three ssDNA binding sites per hexamer; and (v) a working model of DNA unwinding by the DnaB hexamer is proposed.     

Leucine zipper domain targets cAMP-dependent protein kinase to mammalian BK channels

Large conductance, calcium- and voltage-activated potassium (BK) channels control excitability in many tissues and are regulated by several protein kinases and phosphatases that remain associated with the channels in cell-free patches of membrane. Here, we report the identification of a highly conserved, non-canonical, leucine zipper (LZ1) in the C terminus of mammalian BK channels that is required for cAMP-dependent protein kinase (PKA) to associate with the channel and regulate its activity. A synthetic polypeptide encompassing the central d position leucine residues in LZ1 blocks the regulation of recombinant mouse BK channels by endogenous PKA in HEK293 cells. In contrast, neither an alanine-substituted LZ1 peptide nor a peptide corresponding to another, more C-terminal putative leucine zipper, LZ2, had any effect on regulation of the channels by endogenous PKA. Mutagenesis of the central two LZ1 d position leucines to alanine in the BK channel also eliminated regulation by endogenous PKA in HEK293 cells without altering the channel sensitivity to activation by voltage or by exogenous purified PKA. Inclusion of the STREX splice insert in the BK channel protein, which switches channel regulation by PKA from stimulation to inhibition, did not alter the requirement for an intact LZ1. Although PKA does not bind directly to the channel protein in vitro, mutation of LZ1 abolished co-immunoprecipitation of PKA and the respective BK channel splice variant from HEK293 cells. Furthermore, a 127-amino acid fusion protein encompassing the functional LZ1 domain co-immunoprecipitates a PKA-signaling complex from rat brain. Thus LZ1 is required for the association and regulation of mammalian BK channels by PKA, and other putative leucine zippers in the BK channel protein may provide anchoring for other regulatory enzyme complexes.