Solution structure of recombinant human interleukin-6

Interleukin-6 (IL-6) is a 185 amino acid cytokine which exerts multiple biological effects in vivo and whose dysregulation underlies several disease processes. The solution structure of recombinant human interleukin-6 has now been determined using heteronuclear three and four-dimensional NMR spectroscopy. The structure of the molecule was determined using 3044 distance and torsion restraints derived by NMR spectroscopy to generate an ensemble of 32 structures using a combined distance geometry/simulated annealing protocol. The protein contains five alpha-helices interspersed with variable-length loops; four of these helices constitute a classical four-helix bundle with the fifth helix located in the CD loop. There were no distance violations greater than 0.3 A in any of the final 32 structures and the ensemble has an average-to-the-mean backbone root-mean-square deviation of 0.50 A for the core four-helix bundle. Although the amino-terminal 19 amino acids are disordered in solution, the remainder of the molecule has a well defined structure that shares many features displayed by other long-chain four-helix bundle cytokines. The high-resolution NMR structure of hIL-6 is used to rationalize available mutagenesis data in terms of a heteromeric receptor complex.

Complete 1H, 15N and 13C assignments, secondary structure, and topology of recombinant human interleukin-6

Essentially complete backbone and side-chain 1H, 15N and 13C resonance assignments for the 185-amino-acid cytokine interleukin-6 (IL-6) are presented. NMR experiments were performed on uniformly [15N]- and [15N,13C]-labeled recombinant human IL-6 (rIL-6) using a variety of heteronuclear NMR experiments. A combination of 13C-chemical shift, amide hydrogen-bond exchange, and 15N-edited NOESY data allowed for analysis of the secondary structure of IL-6. The observed secondary structure of IL-6 is composed of loop regions connecting five alpha-helices, four of which are consistent in their length and disposition with the four-helix bundle motif present in other related cytokines and previously postulated for IL-6. In addition, the topology of the overall fold was found to be consistent with a left-handed up-up-down-down four-helix bundle based on a number of long-range interhelical NOEs. The results presented here provide deeper insight into structure-function relationships among members of the four-helix bundle family of proteins.

Solution structure of a cellulose-binding domain from Cellulomonas fimi by nuclear magnetic resonance spectroscopy

Multidimensional, multinuclear nuclear magnetic resonance spectroscopy combined with dynamical simulated annealing has been used to determine the structure of a 110 amino acid cellulose-binding domain (CBD) from Cex, a beta-1,4-glycanase from the bacterium Cellulomonas fimi (CBDcex). An experimental data set comprising 1795 interproton NOE-derived restraints, 50 phi, 34 chi 1, and 106 hydrogen bond restraints was used to calculate 20 final structures. The calculated structures have an average root-mean-square (rms) deviation about the mean structure of 0.41 A for backbone atoms and 0.67 A for all heavy atoms when fitted over the secondary structural elements. Chromatography, ultracentrifugation, and 15N NMR relaxation experiments demonstrate that CBDcex is a dimer in solution. While attempts to measure NOEs across the dimer interface were unsuccessful, a computational strategy was employed to generate dimer structures consistent with the derived data set. The results from the dimer calculations indicate that, while the monomer topologies produced in the context of the dimer can be variable, the relative positioning of secondary structural elements and side chains present in the monomer are restored upon dimer formation. CBDcex forms an extensive beta-sheet structure with a beta-barrel fold. Titration with cellohexaose, [beta-D-glucopyranosyl-(1,4)]5-D-glucose, establishes that Trp 54 and 72 participate in cellulose binding. Analysis of the structure shows that these residues are adjacent in space and exposed to solvent. Together with other proximate hydrophilic residues, these residues form a carbohydrate-binding cleft, which appears to be a feature common to all CBDs of the same family.

[Reversal of the inhibitory effect of electroacupuncture on the nociceptive response of neurons in parafascicular nucleus by naloxone and atropine in acute arthritic rats]

Rats with adjuvant arthritis were used as an animal model of pathological pain in this experiment and the nociceptive response of neurons in parafascicular nucleus (Pf) were recorded and intracerebroventricular (icv) injection of naloxone and atropine was adopted in order to investigate the effect of electroacupuncture (EA) and to analyze the neurotransmitters involved. The main results were as follows: (1) The nociceptive response of the majority of Pf neurons (29/34) in arthritic rats was significantly inhibited by EA at acupoints of "Zusanli" and "Sanyinjiao"; (2) The inhibitory effect of EA was reversed in 12/13 units by icv injection of naloxone (4 micrograms/10 microliters); (3) The inhibitory effect of EA was also reversed in 11/12 units by icv injection of atropine (5 micrograms/10 microliters) (4) The spontaneous unit discharge of Pf neurons in arthritic rats was increased after icv injection of naloxone or atropine. Experimental results suggest that EA could have an inhibitory effect on the nociceptive response of Pf neurons in arthritic rats, which might be mediated by opioid system and cholinergic system in the brain, and that opioid system and cholinergic system might have a tonic inhibitory effect on the spontaneous unit discharge of Pf neurons in arthritic rats.

The isolation and structural elucidation of four novel triterpene lactones, pseudolarolides A, B, C, and D, from Pseudolarix kaempferi

Four novel triterpene lactones, pseudolarolides A [1], B [2], C [3], and D [4], were isolated from the seeds of Pseudolarix kaempferi. Their structures and stereochemistry were elucidated from spectral data. Compound 2 shows potent cytotoxicity against three human cancer cell lines, KB (nasopharyngeal), A-549 (lung), and HCT-8 (colon), and against a murine leukemia cell line (P-388) with ED50 values of 0.49, 0.67, 0.73, and 0.79 micrograms/ml, respectively.

Transmembrane region of wild-type and mutant M13 coat proteins. Conformational role of beta-branched residues

Although transmembrane (TM) segments of integral membrane proteins are putatively alpha-helical in conformation, beta-sheet promoters (Val, Ile, Thr) often account for approximately 40% of TM residue composition. We are examining the conformational role(s) of these residues, using as a model system the major coat protein of the filamentous bacteriophage M13. This 50-residue protein, which is located at the Escherichia coli host membrane during phage reproduction, contains a prototypic 19-residue hydrophobic midregion (residues 21-39: YIGYAWAMVVVIVGATIGI). Using "Eckstein" site-directed mutagenesis, we have generated several viable M13 coat protein mutants with beta-branched amino acid substitutions within their TM region. Mutant coat proteins, including Ile32----Val (I32V) and Ala27----Thr (A27T), were obtained in milligram quantities by growing M13 mutant phages in liter preparations, confirming that these coat proteins are capable of assuming their normal biological function(s) in phage reproduction. Circular dichroism spectroscopy performed in the membrane-mimetic medium of deoxycholate micelles indicated comparable alpha-helical contents of mutants I32V and A27T to wild-type protein. 13C nuclear magnetic resonance experiments with mutant A27T demonstrated that the combination of additional beta-branched content and introduction of an -OH substituent induced chemical shift and temperature-dependent changes and influenced the local protein environment at sites up to 12 residues remote from the mutation site. In contrast, mutant I32V (of which a salient feature is a mid-TM pentavaline segment) behaved very similarly to wild-type coat. These findings are interpreted in terms of the range of TM secondary structure and stability which can be accommodated by viable M13 coat protein mutants.

[Involvement of locus coeruleus and dorsal raphe nucleus in the reduction of intragastric pressure induced by ACR stimulation]

The effect of electrical stimulation of hypothalamic arcuate nucleus (ARC) on intragastric pressure (IGP) was observed on 80 Wistar rats anaesthetized with urethan. The main results are as follows: (1) Electrical stimulation of ARC could cause an obvious decrease of IGP. (2) The reduction of IGP induced by electrical stimulation of ARC was not affected by intracerebroventricular injection of naloxone. (3) After lesioning of locus coeruleus or dorsal raphe, the effect of ARC stimulation was depressed. The results suggest that the locus coeruleus and dorsal raphe nucleus may be involved in the reduction of IGP induced by ARC stimulation, but without the involvement of beta-endorphinergic neurons.

[Effects of stimulation of arcuate nucleus on intragastric pressure and peripheral pathway analysis in rats]

The effect of electrical stimulation of arcuate nucleus (ARC) on intragastric pressure (IGP) was examined on 68 Wistar rats anaesthetized with urethan. The results were as follows: (1) Stimulation of ARC could induce an obvious decrease of IGP. (2) This effect was not blocked by atropine but partially by vagotomy. (3) Extirpation of celiac neural plexus or intramuscular injection of phentolamine could obviously reduce the suppression of IGP induced by ARC stimulation, but intramuscular injection of propranolol had no such effect. (4) After vagotomy plus extirpation of celiac neural plexus, IGP could still be made a decrease by stimulating ARC. In view of the present investigation, it is suggested that (1) Both sympathetic nerve and vagus are involved in the reduction of IGP induced by ARC stimulation, the former and the latter routes being respectively mediated by alpha-adrenoceptor and non-cholinergic, non-adrenergic fibres. (2) Humoral factors may be also involved in this effect of ARC stimulation.

Conformations of neurotensin in solution and in membrane environments studied by 2-D NMR spectroscopy

Two-dimensional HOHAHA and ROESY nuclear magnetic resonance techniques are used to obtain complete proton resonance assignments and to perform a conformational investigation of the neuropeptide neurotensin (pGlu-Leu-Tyr-Glu-Asn-Lys-Pro-Arg-Arg-Pro-Tyr-Ile-Leu) in aqueous solution, methanol, and membrane-mimetic [deuterated sodium dodecylsulfate (SDS)] environments. Results suggest the absence of discernible elements of secondary structure in water and methanol. ROESY spectra confirm that Lys-Pro and Arg-Pro peptide bonds are all-trans, but that a significant population of cis Arg-Pro bonds arises in aqueous solution, which increases in the environment of SDS micelles. The conformational ensemble of the peptide is observed to narrow as it becomes bound through its cationic mid-region to SDS micelles, with the accompanying advent of local extended structure. The overall results indicate the inherent conformational flexibility of neurotensin, and emphasize the environmental dependence of conformation in peptides of medium length.

Conformation of proline residues in bacteriorhodopsin

Proline, noted as a hydrophilic residue with helix-breaking potential, nevertheless occurs widely in putatively alpha-helical transmembrane segments of many transport proteins. Ligand-activated or enzyme-assisted trans/cis isomerization of an X-proline peptide bond (where X = any amino acid)--a dynamic, reversible event which could alter the orientation of a transmembrane alpha-helix--may provide the molecular basis for a protein channel regulatory process. Further elucidation of such a function requires knowledge of the isomeric status of the X-Pro bonds in native conformations of membrane proteins. We have used 13C nuclear magnetic resonance (NMR) spectroscopy to examine the conformation of intramembranous X-Pro peptide bonds in biosynthetically-labelled samples of a model transport protein, bacteriorhodopsin (bR) (purple membrane). Spectra of 13C-Tyr-carbonyl labelled bR (in the solvent system CHCl3:CD3OD (1:1) + 0.1 M LiClO4) first established that all 11 bR Tyr residues were sufficiently mobile for their resonances to be detected and resolved, independent of their domain location within the bR sequence. By taking advantage of the known diagnostic chemical shifts of the isomers of Pro-C gamma carbon resonances, spectra of bR labelled with 13C gamma-Pro were then used to demonstrate that all 11 bR X-Pro peptide bonds--including those within the protein's membrane domain (Pro50, Pro91, Pro186)--are in the trans conformation in resting state bR.

[An investigation on adrenergic receptors in rat stomach]

The effects of phentolamine and propranolol on intragastric pressure were observed in 46 Wistar rats. The results showed that: (1) phentolamine did not cause significant changes in the intragastric pressure of intact rats, but, it could obviously decrease the intragastric pressure of rats with vagotomy. (2) propranolol increased the intragastric pressure of intact rats or rats with vagotomy. We concluded that (1) tonic action of adrenergic nerves in stomach is mainly inhibitory; (2) beta-adrenoceptors, which may be present on the smooth muscle of stomach mediate sympathetic inhibition; (3) alpha-adrenoceptors, which come into play through vagus, mediate inhibition, but alpha-adrenoceptors, which may be present on the smooth muscle, mediate sympathetic excitation.

[Establishment and experimental study of a transplantable hepatocellular carcinoma model in 615-strain mice (H 615)]

H 615, the first transplantable mouse liver carcinoma model established in China, was derived from a spontaneous hepatocellular carcinoma of an inbred 615 mouse and has been successfully propagated for 52 generations during the past 7 years and more. Its biologic and pathologic features are relatively stable. H 615 was a syngenic transplantable tumor model of 615-strain mice with a successful transplantation rate of 85.6% without spontaneous regression. The course of tumor growth after subcutaneous inoculation was divided into 4 stages: latent, slowly growing, rapidly growing and terminal stages. Cancer metastasis was rare. The tumor-bearing host would die of cachexia finally. The mean survival time was 62.2 +/- 11.0 days regardless of sex or age. Histologically and ultrastructurally, H 615 was a well-differentiated hepatocellular carcinoma, rather resembling human liver carcinoma. The short-term primary passage culture of H 615 showed that, in vitro, tumor tissue could easily grow into monolayer, the majority of which appeared as epithelioid cells in cytomorphology. Therapeutic tests of 15 anticancer drugs showed that H 615 was sensitive, in varying degrees, to 5 drugs, i. e. MMC, Thio-Tepa, 5FU, CPT and DACT. The inhibition rate of MMC and Thio-Tepa could be as high as 100%. These experimental results are similar to those of the human liver cancer chemotherapy. Hence, the authors believe that H 615 may be a useful model in experimental study of the liver cancer and screening of anticancer drugs.