Basic fibroblast growth factor is a beta-rich protein

The conformation of the 153-residue form of human basic fibroblast growth factor (bFGF) was studied with circular dichroism (CD) and sequence prediction methods. The far-UV CD spectrum with a minimum at 202 nm resembled that of an unordered polypeptide/protein or a protein rich in distorted antiparallel beta-sheets. Analysis of the CD spectrum by the least-squares method of Chang et al. (1978) and the CONTIN program of Provencher and Glöckner (1981) suggested that about one half of the molecule consisted of beta-sheet and there was no alpha-helix. These estimates agreed with the prediction by the sequence method of Garnier et al. (1978) using decision constants based on CD results. bFGF had an unusual CD band at 187 nm, which disappeared upon ionization of Tyr side chains at pH 11.7. It also had another unusual property of irreversibly converting the CD spectrum to a helix-like one with a double minimum at 205 and 215 and a maximum at 189 nm upon heating the solution to above 55 degrees C. The helicity was also enhanced in trifluoroethanol and in sodium dodecyl sulfate. The mutant bFGF in which cysteines 76 and 94 were replaced by serine residues had essentially the same properties as the wild-type.

Quantitative analysis of nonoxynol-9 in blood

At present, there is little data on the level of nonoxynol-9 (N-9) in blood. Using routine methods, the rate of recovery for N-9 in blood has been confirmed to be very low. A method determining N-9 levels in urine has been found but obviously a more efficient method for determining N-9 levels in blood and urine is still needed. Here, a method of determining N-9, a nonionic surfactant spermicide, in blood is presented. The analytical procedure is a simple and convenient method. Using HPLC, UV detector, ODS reversed-phase column, methanol-water mobile phase, NaCl salting-out and two extractions with benzene, a rate of recovery for N-9 of 93 +/- 4% has been obtained.

Evidence that the head of kinesin is sufficient for force generation and motility in vitro

Kinesin is a mechanochemical protein that converts the chemical energy in adenosine triphosphate into mechanical force for movement of cellular components along microtubules. The regions of the kinesin molecule responsible for generating movement were determined by studying the heavy chain of Drosophila kinesin, and its truncated forms, expressed in Escherichia coli. The results demonstrate that (i) kinesin heavy chain alone, without the light chains and other eukaryotic factors, is able to induce microtubule movement in vitro, and (ii) a fragment likely to contain only the kinesin head is also capable of inducing microtubule motility. Thus, the amino-terminal 450 amino acids of kinesin contain all the basic elements needed to convert chemical energy into mechanical force.

Conformation of acetylcholine receptor in the presence of agonists and antagonists

The conformations of acetylcholine receptor from Torpedo californica in the absence and presence of agonists, antagonists, and local anesthetics were studied by circular dichroism (CD). Without ligands, the receptor had about 40% helix, 20% beta-sheets, and 10% beta-turns as analyzed from its far-UV CD spectrum. Its near-UV CD spectrum resembled that of acetylcholinesterase from the same source. None of the ligands studied altered the far-UV spectrum of the receptor. However, in the near-UV region, carbamylcholine and acetylcholine shifted the Phe and Tyr bands of AChR to less negative, whereas hexamethonium changed the Tyr bands to more negative, indicating that the site of binding of agonists and antagonists and their effect on the conformation of the receptor may be different. Decamethonium, procaine, and lidocaine had no effect on both the far- and near-UV CD spectra of acetylcholine receptor.

Opioid-binding protein (OBCAM) is rich in beta-sheets

Based on circular dichroism (CD) and the sequence-predictive method, the opioid-binding cell adhesion molecule (OBCAM) consisted of one half beta-sheets and one fourth alpha-helices. This is consistent with significant sequence homology of the protein to several members of the immunoglobulin (Ig) superfamily, particularly cell adhesion molecules, which are rich in beta-sheets. Hydropathy analysis suggests that hydrophobic and hydrophilic regions were evenly distributed along the sequence, but the NH2- and COOH-termini were hydrophobic. Hydrophobic moments and Fourier-transform amphipathic analyses further suggest that residues 23-30 and 83-93 were amphipathic beta-sheets. The overall conformation of OBCAM was unaltered by adding linoleic acid, which is required for opioid ligand binding.

Thermal unfolding of helices of a C-peptide analogue of ribonuclease A in sodium dodecyl sulfate solution

The conformation of a 13-residue C-peptide analogue of ribonuclease A, suc-AET-AAAKFLRAHA-CONH2, in NaDodSO4 solutions with respect to temperature was studied with CD. The equilibrium constant of unfolding yielded a straight line in a van't Hoff plot. In 10 mM NaDodSO4, delta G mu = 120 cal/mol, delta H mu = 700 cal/mol, and delta S mu = 2.0 entropy units all on per helical residue. These values compared fairly well with the thermodynamic parameters of the uncharged helix-coil transition of (Glu)n in 0.1 M NaCl based on the theories of Zimm and Bragg and Zimm and Rice. The peptide was not unfolded at 75 degrees C completely. Even in water without surfactant it was not a "random coil."

Transfer of foreign genes by electroporation and their expression in mammalian cells

Expression of foreign genes transferred into mammalian cells by electroporation has been studied. The pX1TK gene, pSV2Neo gene and pUCEJ oncogene have been introduced into MLTK- cells and NIH/3T3 cells, respectively. Stable transformation transient expression of TK gene by MLTK- cells as well as stable and malignant transformation of NIH/3T3 cells have been obtained. Transient expression frequency is about 80% and stable transformation frequency is about 10(-4). Integration of foreign genes into the cellular genome was verified with molecular hybridization. Tumor development was observed after inoculation of transformed cells into nude mice.

Preparation of clear solutions of reconstituted acetylcholinesterase. Effect of ionic strength and lipid/protein ratio

The detergent-soluble globular dimer of acetylcholinesterase from Torpedo californica was reconstituted through dialysis into preformed egg phosphatidylcholine vesicles. The formation of the enzyme-lipid complexes depended on the ionic strength of the dialysis buffer as well as the molar lipid/protein ratio (R). The enzyme was unstable at I less than 0.05; increasing the ionic strength increased the size of the complex. A too low R value (e.g. 1000) would promote self-aggregation of the enzyme and produce heterogeneous complexes, especially at high I values. On the other hand, a too high R value (e.g. greater than 5000) favored the formation of large enzyme-lipid complexes; their solutions were too turbid for optical studies. The enzyme reconstituted at I = 0.07 and R = 4000 gave a clear solution and showed no artifacts due to light scattering. The conformation based on circular dichroism and enzymatic activity of the detergent-soluble enzyme were unchanged upon reconstitution. The reconstituted enzyme in lipid vesicles seemed to be slightly more stable against thermal denaturation than the protein in sodium cholate solution.

Identification of globular mechanochemical heads of kinesin

Kinesin is a mechanoenzyme which uses energy liberated from ATP hydrolysis to transport particles towards the 'plus ends' of microtubules. The enzyme consists of two polypeptide heavy chains of relative molecular mass (Mr) approximately 110,000-140,000 (110K-140K) plus copurifying light chains; these polypeptides are arranged in a structure consisting of two globular heads attached to a fibrous stalk which terminates in a 'feathered' tail. Here we report that a function-disrupting monoclonal antikinesin, which binds to the 45K fragment of the kinesin heavy chain, recognizes an epitope located towards the N-terminal end of the heavy chain, and decorates the two globular heads lying at one end of the intact molecules (one antibody per head). The results show that the two heavy chains of native kinesin are arranged in parallel, and that the 45K fragments, which display nucleotide-sensitive interactions with microtubules, represent mechanochemical 'heads' located at the N-terminal regions of the heavy chains. Thus, it is likely that the kinesin heads are analogous to the subfragment-1 domains of myosin.

A three-domain structure of kinesin heavy chain revealed by DNA sequence and microtubule binding analyses

The structure and function of kinesin heavy chain from D. melanogaster have been studied using DNA sequence analysis and analysis of the properties of truncated kinesin heavy chain synthesized in vitro. Analysis of the sequence suggests the existence of a 50 kd globular amino-terminal domain that contains an ATP binding consensus sequence, followed by another 50-60 kd domain that has sequence characteristics consistent with the ability to fold into an alpha helical coiled coil. The properties of amino- and carboxy-terminally truncated kinesin heavy chains synthesized in vitro reveal that a 60 kd amino-terminal fragment has the nucleotide-dependent microtubule binding activities of the intact kinesin heavy chain, and hence is likely to be a "motor" domain. Finally, the sequence data indicate the presence of a small carboxy-terminal domain. Because it is located at the end of the molecule away from the putative "motor" domain, we propose that this domain is responsible for interactions with other proteins, vesicles, or organelles. These data suggest that kinesin has an organization very similar to that of myosin even though there are no obvious sequence similarities between the two molecules.

Tacrine protection of acetylcholinesterase from inactivation by diisopropylfluorophosphate: a circular dichroism study

Tacrine (1,2,3,4-tetrahydro-9-aminoacridine) showed an apparent noncompetitive inhibition of Torpedo acetylcholinesterase (AChE) with a dissociation constant, Ki, of 8.5 nM. It altered the CD bands of AChE in the near-UV region, which monitor the local conformation of aromatic side groups, but not those in the far-UV region, which measure the secondary structure. An extrinsic CD band was induced at 348 nm, with a molar ellipticity of 35,000 deg cm2 dmol-1 (bases on tacrine), when each AChE subunit (Mr = 67,000) was saturated with one tacrine (mol/mol). With this band as a probe, the bound tacrine could be displaced by edrophonium or decamethonium, both of which are known to bind to the anionic site at the active center of AChE, but not by propidium, which binds to the peripheral site of the enzyme. Tacrine protected AChE from inactivation by diisopropylfluorophosphate (DFP). AChE completely lost its enzymatic activity when 1 mol of DFP was bound per mol of subunit upon incubation of 7 microM AChE (subunit) with 100 microM DFP for 40 min, but tacrine-treated AChE retained 60% of its activity and bound only 0.2 mol of DFP per mol of subunit under similar conditions. The corresponding CD, at 348 nm, of the AChE-tacrine-DFP complex increased or decreased gradually, depending on the order of addition of tacrine and DFP, and reached an equilibrium value (80% of its original) after 2 days. The difference absorption spectrum of the AChE-tacrine-DFP complex was the same as that of the AChE-tacrine complex. These results suggest that the protective effect of tacrine may be due to steric hindrance at the esteratic site of the enzyme.

Isolation and characterization of the gene encoding the heavy chain of Drosophila kinesin

An antiserum that recognizes the heavy chain of Drosophila kinesin was used to isolate Drosophila cDNA clones. Immunoblot analysis of the proteolytic fragments of the protein produced by one of the cDNA clones has demonstrated that the cDNA clones encode the heavy chain of Drosophila kinesin. The in vitro-synthesized product of the largest cDNA comigrates with Drosophila kinesin heavy chain on NaDodSO4/polyacrylamide gels and binds to taxol-stabilized microtubules in the presence of the nonhydrolyzable analogue of ATP, 5'-adenylyl imidodiphosphate, but not in the presence of ATP or 0.1 M KCl. Analysis of the cDNA clones suggests that there is a single gene encoding kinesin heavy chain in Drosophila located at polytene chromosome position 53A. However, Southern hybridization analyses suggest the presence of related sequences in the Drosophila genome.

Conformation similarities of ricin A-chain and trichosanthin

The conformation of ricin A-chain from castor bean was studied by circular dichroism at pH 4.7, 7 and 9 and compared with that of trichosanthin from the Chinese herb Tianhuafen. The CD spectra of ricin A-chain and trichosanthin were nearly identical at each of the three pHs. Analysis of the data indicated that, like trichosanthin, ricin A-chain had about 29% alpha-helix and 42% beta-sheet but no beta-turn. However, there was a subtle difference in the CD spectra in 20 mM sodium dodecyl sulfate, the addition of which at pH 7 slightly increased the helicity and decreased the content of beta-sheet of ricin A-chain in contrast to a larger increase in helicity at the expense of beta-sheet for trichosanthin, thus indicating a different stability against the surfactant. Native ricin A-chain and trichosanthin had about the same amount of secondary structure, which supports the belief that a high degree of sequence homology of the two proteins [Zhang & Wang (1986) Nature 321, 477-478] may lead to a conformational similarity between them, even though the two proteins are not taxonomically related.

Conformation similarities of the globular and tailed forms of acetylcholinesterase from Torpedo californica

The conformation of the globular dimer (G2), the tailed asymmetric dodecamer (A12, also containing some tailed octamer A8) and the globular tetramer (G4, prepared by removing the collagen-like tail from A12) of acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) was studied by circular dichroism (CD) in the ultraviolet region. The G2 and G4 forms had similar conformation with about 40% alpha-helix, 35% beta-sheets and 4% beta-turns; the tailed form had a lower helicity (about 34%) and beta-form (about 25%) content probably because of the presence of the tail whose CD spectrum resembles that of an unordered form, but it had about the same amount of beta-turns as the other two forms. All three forms also had similar CD spectra in the near-ultraviolet region due to their non-peptide chromophores. The pH, thermal and urea denaturation of the three acetylcholinesterase forms was also similar to each other. The pH-dependency of both the enzymatic activity and CD intensity of the three forms showed bell-shaped curves with a plateau at pH 7-8. The activity was completely lost at pH below 5 or above 10, but the corresponding CD spectra retained 70-80% of the original magnitudes. Thermal denaturation of the three forms at pH 7.5 showed a conformational transition and loss of activity between 30 and 40 degrees C, but the CD intensity of the helical band at 222 nm was reduced by only 20-30%. Urea denaturation of the three forms began at 1 M urea; it was protein concentration- and time-dependent. Again, the activity disappeared faster than the decreasing CD intensity. Thus, the overall conformation of the three acetylcholinesterase forms appears to be relatively stable, but their active site is easily perturbed by changing the environment. The loss of activity correlated well with the disappearance of the CD band of tryptophan(s) in the near-ultraviolet region, suggesting that the Trp residue(s) might be at or near the active center of the enzyme.

Interaction of snake venom cardiotoxin (a membrane-disruptive polypeptide) with human erythrocytes

The action of 7.2 microM cardiotoxin on 0.25% human erythrocytes in a plasma extender solution was studied by the interaction of toxin with intact red blood cells and subsequent hemolysis of the cells. The binding of toxin to cells was completed within 10 min, whereas the membrane rigidity was weakened in a non-lytic period for about 25 min. The toxin molecules bound almost exclusively to the membrane. The bound toxin could not be liberated with either 0.5% Triton X-100 or 0.1 N NaOH. The degree of binding was slightly reduced in the presence of 10 mM mono- and divalent inorganic salts. The action of toxin might weaken the in situ association of several proteins that are linked with band 3 protein of the membrane, thus making the cells fragile and altering the shape of the cell to a smooth sphere.

Conformation of abortifacient proteins: trichosanthin, alpha-momorcharin and beta-momorcharin

The conformations of three abortifacient proteins, trichosanthin from the Chinese herb Tianhuafen and alpha- and beta-momorcharin from the Chinese herb Kuguazi, were studied by circular dichroism. Their spectra in the ultraviolet region (188-250 nm) were similar to each other and also pH-independent (between pH 5 and 9). All three proteins contained about 30% helix, as compared with 39% for trichosanthin by X-ray diffraction study, and 40-60% beta-sheets, but had no beta-turns, suggesting a structural homology among the proteins. The addition of 20 mM sodium dodecyl sulfate nearly doubled the helicity of beta-momorcharin at the expense of beta-sheets but had a small effect on the conformation of alpha-momorcharin, whereas the corresponding change in conformation for trichosanthin was in between the two momorcharins. This implies a marked difference in stability of the three proteins against the surfactant.

Competitive binding of dynorphin-(1-13) and beta-endorphin to cerebroside sulfate in solution

Circular dichroism was used as a probe for competitive binding of two opioid peptides, dynorphin-(1-13) and beta-endorphin, with cerebroside sulfate, a membrane lipid thought to be part of the morphine receptor complex. The rationale was that bound beta-endorphin is partially helical but bound dynorphin-(1-13) remains unordered, thus making it possible to detect the degree of binding of beta-endorphin. The addition of dynorphin-(1-13) to a cerebroside sulfate solution of beta-endorphin invariably displaced beta-endorphin from the peptide-lipid complex, but the addition of beta-endorphin had little effect on dynorphin-(1-13) bound to the lipid. Similar results were obtained for competitive binding of the two peptides with two other amphiphiles, sodium dodecyl and decyl sulfate. The maximum number of binding sites on dynorphin-(1-13) and beta-endorphin was between five and six, which coincides with the five positively charged side chains plus an alpha NH+3 group at the NH2 terminus on both peptide molecules. The results support our working hypothesis that dynorphin-(1-13) may displace beta-endorphin bound to the receptor, which in turn can account for the inhibition of beta-endorphin-induced analgesia by dynorphin-(1-13).

The formaldehyde-donating activity of N5,N10-methylene tetrahydrofolic acid in xenobiotic biotransformation

Reaction of reproterol, (7-(3-[2-(3,5-dihydroxyphenyl)-2-hydroxyethylamino]propyl)theophyl line (I), with formaldehyde liberated in a solution of N5,N10-methylene tetrahydrofolic acid at pH 7.3 led to the formation of 7-[3-(4,6,8-trihydroxy-1,2,3,4-tetrahydroisoquinolinyl-2)propyl]th eophylline (II), but no such reaction was observed in a solution of N5-methyl tetrahydrofolic acid. Compound II was also formed by incubation of I with rat-liver subcellular fractions. The highest formaldehyde-donating activity was found in the soluble fraction but some activity was also observed with washed mitochondria and microsomes. Dimedone was transformed to methylene bisdimedone by incubation with the soluble fraction. The amount of formaldehyde liberated in the soluble fraction during a four hour incubation at 22 degrees C was 1-3.6 mumol/g of liver. Metaproterenol and terbutaline, structurally related to I, reacted with formaldehyde to yield the corresponding tetrahydro-isoquinolines. The rate of this chemical reaction for the three drugs correlated with the amount of the tetrahydroquinolines formed by incubation with the soluble fraction and in orally dosed rats.

Bis[cyclo(histidylhistidine)]copper(II) complex that mimicks the active center of superoxide dismutase has its catalytic activity

The formation of copper complexes with bis[cyclo( histidylhistidine )] copper(II) was determined potentiometrically; the maximum coordination number was four deprotonated histidine residues per Cu(II) ion. This complex mimicks the active center of Cu/Zn superoxide dismutase (superoxide:superoxide oxidoreductase, EC 1.15.1.1). Its absorption spectrum showed a broad band above 600 nm as compared with the 670- to 680-nm band of the enzyme. Its CD spectrum had a negative 600- to 605-nm band and a more intense positive band near 780 nm. The band positions were identical with, and the intensities were higher than, those of the enzyme, but the corresponding bands had opposite signs. This can be attributed to the difference in the distorted planar structure between the complex and enzyme. The complex catalyzed the dismutation of superoxide anion; the activity was 1/10th that of the enzyme on a molar basis, but about three times that of the enzyme on a weight basis.

Membrane disintegration and hemolysis of human erythrocytes by snake venom cardiotoxin (a membrane-disruptive polypeptide)

The action of 7.2 microM cardiotoxin on 0.25% (v/v) human erythrocytes in plasma extender solution was studied by osmotic fragility and hemolysis. The toxin loosened the membrane rigidity without lysis for about 25 min and then the cells hemolyzed for about 6 h at 37 degrees. The membrane was not perturbed at 15 degrees. The hemolysis of cells was optimal at 37 degrees and virtually stopped below 20 degrees. Both events could be suppressed by adding inorganic salts or toxin antibody. Once the membrane was loosened, the addition of phospholipase A2 would potentiate the disintegration of erythrocytes. In contrast, hemolysis of erythrocytes by (Lys)n lacked a non-lytic period and was temperature independent and insensitive towards salts and phospholipase A2.