13C and 1H NMR studies of helix-coil transition of poly(β-benzyl-L-aspartate) and poly(γ-benzyl-L-glutamate): Behavior in nonprotonating solvent mixtures,and origin of solvent-induced chemical shift

From the results of ¹³C-nmr measurement of poly(β-benzyl-L -aspartate) and its model compounds in dimethyl sulphoxide/deuterated chloroform mixtures, it was found that the side chain of poly(β-benzyl-L -aspartate) is solvated by dimethyl sulphoxide in the region more than dimethyl sulphoxide 20% (v/v), where the backbone maintains the α-helix. The chemical shift differences in the benzyl group carbons of poly(γ-benzyl-L -glutamate) (trifluoroacetic acid/deuterated chloroform) accompanied by the helix-coil transition, originate from the interaction between the ester group of the side chain and trifluoroacetic acid. The chemical shift difference in the ester carbon is similar. On the other hand, the chemical shift differences of the side-chain carbons in the alkyl portion (C^β, C^γ) originate not only from the interaction between the ester group of the side chain and trifluoroacetic acid, but also from some other unknown factors. The chemical shift differences of the side-chain carbons of poly(β-benzyl-L -aspartate) originate from the interaction between the ester group of the side chain and trifluoroacetic acid.     

IL-4-supported induction of cytolytic T lymphocytes requires IL-2 and IL-6

Previous work indicated that a CTL response can be generated by the combination of IL-2 plus IL-6 or IL-4 alone. Because of the ubiquitous production of IL-6 and its apparent ability to induce IL-2, we explored the interdependence of these lymphokines in supporting a CTL response from murine thymocytes. For thymocytes cultured in IL-4, further addition of IL-6 enhanced thymocyte proliferation. In addition, a role for IL-6 in thymocyte activation was indicated by the ability of anti-IL-6 mAb to block both IL-4-directed proliferation and the cytotoxic response found in the presence of IL-4. The addition of IL-2 to limiting doses of IL-4 augmented the CTL response; however, the response to high levels of IL-4 was not augmented by addition of IL-2. Consistent with this apparent involvement of IL-2 in the IL-4-mediated response we found: (a) that mAb to IL-2 significantly reduced the CTL response generated in the presence of IL-4; (b) that IL-2 activity was present in culture supernatant following incubation of thymocytes with high levels of IL-4; and (c) that enhanced IL-2 receptor expression found in the presence of IL-4 was blocked with the addition of anti-IL-2 antibody to the thymocyte culture. In contrast to the data for proliferation, anti-IL-4 mAb had no effect on the generation of CTL in the presence of IL-2 + IL-6 but readily blocked the CTL response to IL-4. These results indicate that, for thymocyte responders, the CD8+ CTL generated in the presence of IL-4 require both IL-2 and IL-6.     

Phosphorylation of smg p21B/rap1B p21 by cyclic GMP-dependent protein kinase.

smg p21B/rap1B p21, a member of ras p21-like small GTP-binding protein superfamily, has been shown to be phosphorylated by cyclic AMP-dependent protein kinase (protein kinase A). We show here that this protein was also phosphorylated by cyclic GMP-dependent protein kinase (protein kinase G) in a cell-free system. The same serine residue (Ser179) in the C-terminal region was phosphorylated by both protein kinases G and A. The Km and Vmax values of smg p21B for protein kinase G were 5 x 10(-7) M and 4 x 10(-9) mol/min/mg, and those values for protein kinase A were 1 x 10(-7) M and 3 x 10(-8) mol/min/mg.     

Regulation of the superoxide-generating NADPH oxidase by a small GTP-binding protein and its stimulatory and inhibitory GDP/GTP exchange proteins.

The superoxide-generating NADPH oxidase system in phagocytes consists of at least membrane-associated cytochrome b558 and three cytosolic components named SOCI/NCF-3/sigma 1/C1, SOCII/NCF-1/p47-phox, and SO-CIII/NCF-2/p67-phox. p47-phox and p67-phox were isolated, and their primary structures were determined, but SOCI has not been well characterized. In the present study, we first purified SOCI to homogeneity from the cytosol fraction of the differentiated HL-60 cells. The purified SOCI was a small GTP-binding protein (G protein) with a M(r) of about 22,000. The guanosine 5'-(3-O-thio)triphosphate-bound form, but not the GDP-bound form, of this small G protein showed the SOCI activity. The partial amino acid sequence of SOCI thus far determined was identical to the amino acid sequence deduced from the cDNA encoding rac2 p21. None of the purified small G proteins, including Ki-ras p21, smg p21B/rap1B p21, rhoA p21, and rac1 p21, showed the SOCI activity. These results indicate that SOCI is a small G protein very similar, if not identical, to rac2 p21. The GDP/GTP exchange reaction of SOCI was stimulated and inhibited by stimulatory and inhibitory GDP/GTP exchange proteins for small G proteins, named smg GDS and rho GDI, respectively. The NADPH oxidase activity was also stimulated and inhibited by smg GDS and rho GDI, respectively. These results indicate that the superoxide-generating NADPH oxidase system is regulated by both smg GDS and rho GDI through rac2 p21 or the rac2-related small G protein in phagocytes.     

A possible target protein for smg-25A/rab3A small GTP-binding protein.

The smg-25A/rab3A protein (smg p25A) is a small GTP-binding protein implicated in intracellular vesicle traffic, particularly in neurotransmitter release from the presynapse. In the present study, we attempted to identify a target protein in bovine brain crude membranes that might be interacted with the GTP-bound form of smg p25A. When the guanosine-5'-(3-O-thio)triphosphate (GTP gamma S)-bound form of radioiodinated smg p25A and the crude membrane fraction of bovine brain were incubated with a cross-linker, disuccinimidyl suberate, and the sample was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) followed by autoradiography, one radioactive band with a M(r) of about 110,000 was detected. This radioactive band appeared to be composed of radioiodinated smg p25A and a molecule with a M(r) of about 86,000. This molecule, tentatively termed here smg p25A target, was extracted from the membranes by a detergent and highly purified by column chromatographies and sucrose density gradient ultracentrifugation. The purified smg p25A target was sensitive to heat boiling and tryptic digestion, indicating that smg p25A target is a protein molecule. The M(r) of the purified smg p25A target was estimated to be about 85,000-86,000 from SDS-PAGE and to be about 100,000 from the S value. The cross-linking of radioiodinated smg p25A with the purified smg p25A target was inhibited by the GTP gamma S-bound form of non-radioactive smg p25A with an IC50 of about 8 nM. The GDP-bound form of smg p25A was much less effective. Other small GTP-binding proteins, such as c-Ki-ras p21, rhoA p21, smg p21B, and rab11 p24 were ineffective. These results indicate that a protein with a M(r) of about 85,000-100,000 is a target for smg p25A.     

Construction of shuttle vectors derived fromAcetobacter xylinum for cellulose-producing bacteriumAcetobacter xylinum

Summary Shuttle vector pUF106 was constructed by ligation ofAcetobacter xylinum plasmid pFF6 toEscherichia coli plasmid pUC18. It had unique restriction sites suitable for insertion of a foreign DNA fragment and conferred ampicillin resistance to a host. pUF106 transformed cellulose-producingA. xylinum ATCC10245 as well asE. coli JM109.     

Tissue and subcellular distributions of an inhibitory GDP/GTP exchange protein (GDI) for the rho proteins by use of its specific antibody

We have recently purified from bovine brain cytosol to near homogeneity a GDP/GTP exchange protein for the rho proteins, named rho GDI, that inhibits the dissociation of GDP from and the subsequent binding of GTP to the rho proteins. In the present study, we made a monoclonal antibody against rho GDI and studied its tissue distribution in rat and its subcellular distribution in rat cerebrum by use of this antibody. rho GDI was found in most rat tissues as described for the rho proteins. In rat cerebrum, rho GDI was mostly found in the cytosol of neuron body and synaptosome. In synaptosome, it was mainly found in the synaptic cytosol.     

Tissue and subcellular distributions of an inhibitory GDP/GTP exchange protein (GDI) for smg p25A by use of its antibody

We have recently purified from bovine brain cytosol to near homogeneity a GDP/GTP exchange protein for smg p25A, named smg p25A GDI, that inhibits the dissociation of GDP from and the subsequent binding of GTP to smg p25A. In the present study, we made an antiserum against smg p25A GDI and studied its tissue distribution in rat and its subcellular distribution in rat cerebrum by use of this antiserum. smg p25A GDI was found in secretory cells with both regulated and constitutive secretion types. Since smg p25A was previously found in only secretory cells with a regulated secretion type, this result suggests that small GTP-binding proteins different from smg p25A but recognized by smg p25A GDI are present in secretory cells with a constitutive secretion type, and that smg p25A GDI is involved in both regulated and constitutive secretory processes. In subcellular fractionation analysis of rat cerebrum, smg p25A GDI was mostly found in the cytosol fraction of neuron body and synaptosome. In synaptosome, it was mainly found in the synaptic cytosol.     

A small GTP-binding protein (G protein) recognized by smg p25A GDP dissociation inhibitor (GDI) in human platelet membranes and GDI for this small G protein in human platelet cytosol

We have recently purified from bovine brain cytosol a novel type of regulatory protein for smg p25A, named smg p25A GDP dissociation inhibitor (GDI), that regulates the GDP/GTP exchange reaction of smg p25A by inhibiting the dissociation of GDP from and thereby the subsequent binding of GTP to it. This smg p25A GDI is inactive for other ras p21/ras p21-like small GTP-binding proteins (G proteins) including c-Ha-ras p21, smg p21, rhoA p21 and rhoB p20. In human platelet membranes, smg p25A was not detected but a G protein with an apparent Mr value of 24,000 (24KG) was recognized by smg p25A GDI and the dissociation of GDP from and the binding of GTP to 24KG were inhibited by smg p25A GDI. The doses of smg p25A GDI necessary for these activities for both 24KG and smg p25A were the same. This 24KG was not recognized by an anti-smg p25A monoclonal antibody. The GDI activity for human platelet 24KG and smg p25A was detected in human platelet cytosol. This human platelet GDI was recognized by an anti-smg p25A GDI polyclonal antibody. These results indicate that there is a 24KG-24KG GDI system similar to a smg p25A-smg p25A GDI system in human platelets.