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C A Royer

Publications and source records attributed to C A Royer.

At least 55 records · Page 3Linked to original sources
PubMed1994

Electrostatic forces contribute to interactions between trp repressor dimers.

The trp repressor of Escherichia coli (TR), although generally considered to be dimeric, has been shown by fluorescence anisotropy of extrinsically labeled protein to undergo oligomerization in solution at protein concentrations in the micromolar range (Fernando, T., and C. A. Royer 1992. Biochemistry. 31:3429-3441). Providing evidence that oligomerization is an intrinsic property of TR, the present studies using chemical cross-linking, analytical ultracentrifugation, and molecular sieve chromatography demonstrate that unmodified TR dimers form higher order aggregates. Tetramers and higher order species were observed in chemical cross-linking experiments at concentrations between 1 and 40 microM. Results from analytical ultracentrifugation and gel filtration chromatography were consistent with average molecular weight values between tetramer and dimer, although no plateaus in the association were evident over the concentration ranges studied, indicating that higher order species are populated. Analytical ultracentrifugation data in presence of corepressor imply that corepressor binding destabilizes the higher order aggregates, an observation that is consistent with the earlier fluorescence work. Through the investigation of the salt and pH dependence of oligomerization, the present studies have revealed an electrostatic component to the interactions between TR dimers.

Bacterial Proteins↗
PubMed1993

Fluorescence anisotropy assays implicate protein-protein interactions in regulating trp repressor DNA binding.

The study of interactions between proteins and nucleic acids is central to the understanding of the control of genetic expression. Fluorescence anisotropy has been used to measure, in solution, the equilibrium binding profiles of a bacterial repressor protein, the tryptophan repressor (TR), to a fluorescently labeled oligonucleotide containing one of its target operator sequences. Investigation of the effects of changing concentrations of corepressor, operator DNA, and protein implicate TR oligomers in the regulation of DNA binding. These studies also demonstrate that the relatively straightforward technique of fluorescence anisotropy can be applied to the study of the interactions between proteins and nucleic acids. The fluorescence technique exhibits sufficient sensitivity to replace radioactive methods of detection in most cases. In addition, since it is a solution-based methodology, it offers a true equilibrium measure of the protein-nucleic acid equilibria, and the effects of changes in solution conditions such as salt and ligand concentration, pH, and temperature can be readily evaluated. Data acquisition is relatively simple and rapid, and the data are of sufficient quality for detailed thermodynamic analyses of complex systems. Given these attributes, fluorescence anisotropy will find multiple applications in the area of genetic regulation.

Bacterial Proteins↗
PubMed1993

Effects of amino acid substitutions on the pressure denaturation of staphylococcal nuclease as monitored by fluorescence and nuclear magnetic resonance spectroscopy.

In the present study we have used high hydrostatic pressure coupled with either time-resolved and steady-state fluorescence or NMR spectroscopy in order to investigate the effects of amino acid substitutions on the high-pressure denaturation properties of staphylococcal nuclease. This protein has been shown previously to be structurally heterogeneous in its native state. On the NMR time scale, four distinct interconverting conformational forms arise from the population of both cis and trans Xaa-Pro peptide bonds (His46-Pro47 and Lys116-Pro117) [Evans et al. (1989) Biochemistry 28, 362; Loh et al. (1991) in Techniques in Protein Chemistry II, pp 275-282, Academic Press, New York]. Mutations in the protein sequence have been shown to change the distribution among the various forms [Alexandrescu et al. (1989) Biochemistry 28, 204; Alexandrescu et al. (1990) Biochemistry 29, 4516]. Time-resolved fluorescence on a series of mutants with altered equilibria for cis/trans isomerism about the 116-117 peptide bond did not reveal any simple relationship between the position of the cis/trans equilibrium in the folded state and the heterogeneity of the fluorescence decay. However, the specific dynamic properties of each mutant, as revealed by time-resolved fluorescence, do appear to be correlated with their partial molar volume changes of denaturation. A striking finding is that mutation of either (or both) of the prolines that exhibits structural heterogeneity to glycine greatly alters the stability of the protein to pressure. These mutations also result in decreased chain mobility as assessed by time-resolved fluorescence. It appears that packing defects, which allow for peptide bond cis/trans heterogeneity in the wild-type protein, are removed by the Pro-->Gly substitutions.

Amino Acid Sequence↗
PubMed1993

Resolution of the fluorescence equilibrium unfolding profile of trp aporepressor using single tryptophan mutants.

Single tryptophan mutants of the trp aporepressor, tryptophan 19-->phenylalanine (W19F) and tryptophan 99-->phenylalanine (W99F), were used in this study to resolve the individual steady-state and time-resolved fluorescence urea unfolding profiles of the two tryptophan residues in this highly intertwined, dimeric protein. The wild-type protein exhibits a large increase in fluorescence intensity and lifetime, as well as a large red shift in the steady-state fluorescence emission spectrum, upon unfolding by urea (Lane, A.N. & Jardetsky, O., 1987, Eur. J. Biochem. 164, 389-396; Gittelman, M.S. & Matthews, C.R., 1990, Biochemistry 29, 7011-7020; Fernando, T. & Royer, C.A., 1992, Biochemistry 31, 6683-6691). Unfolding of the W19F mutant demonstrated that Trp 99 undergoes a large increase in intensity and a red shift upon exposure to solvent. Lifetime studies revealed that the contribution of the dominant 0.5-ns component of this tryptophan tends toward zero with increasing urea, whereas the longer lifetime components increase in importance. This lifting of the quenching of Trp 99 may be due to disruption of the interaction between the two subunits upon denaturation, which abolishes the interaction of Trp 99 on one subunit with the amide quenching group of Asn 32 on the other subunit (Royer, C.A., 1992, Biophys. J. 63, 741-750). On the other hand, Trp 19 is quenched in response to unfolding in the W99F mutant. Exposure to solvent of Trp 19, which is buried at the hydrophobic dimer interface in the native protein, results in a large red shift of the average steady-state emission.(ABSTRACT TRUNCATED AT 250 WORDS)

Apoproteins↗
PubMed1993

Tryptophan replacements in the trp aporepressor from Escherichia coli: probing the equilibrium and kinetic folding models.

Mutants of the dimeric Escherichia coli trp aporepressor are constructed by replacement of the two tryptophan residues in each subunit in order to assess the effects on equilibrium and kinetic fluorescence properties of the folding reaction. The three kinetic phases detected by intrinsic tryptophan fluorescence in refolding of the wild-type aporepressor are also observed in folding of both Trp 19 to Phe and Trp 99 to Phe single mutants, demonstrating that these phases correspond to global rather than local conformational changes. Comparison of equilibrium fluorescence (Royer, C.A., Mann, C.J., & Matthews, C.R., 1993, Protein Sci. 2, 1844-1852) and circular dichroism transition curves induced by urea shows that replacement of either Trp 19 or Trp 99 results in noncoincident behavior. Unlike the wild-type protein (Gittelman, M.S. & Matthews, C.R., 1990, Biochemistry 29, 7011-7020), tertiary and/or quaternary structures are disrupted at lower denaturant concentration than is secondary structure. The equilibrium results can be interpreted in terms of enhancement in the population of a monomeric folding intermediate in which the lone tryptophan residue is highly exposed to solvent, but in which substantial secondary structure is retained. The location of both mutations at the interface between the two subunits (Zhang, R.G., et al., 1987, Nature 327, 591-597) provides a simple explanation for this phenomenon.

Apoproteins↗
PubMed1993

Improvements in the numerical analysis of thermodynamic data from biomolecular complexes.

In this work, recent improvements in the capability of the numerical solver-based binding data global analysis program, BIOEQS, are presented. These improvements represent an expansion of the types of physical models which can be considered. The first realm of improvement concerns the modeling of systems which include several species of the same stoichiometry and differing chemical potentials, or site isomers. Such an option is generally used in the analysis of binding of multiple ligands to multiple protein sites. In addition to classical ligand binding problems, such a capability is useful in considering the binding of protein to different sites on the same DNA molecule and the effects of ligation upon these equilibria. It can also be employed for consideration of the equilibrium unfolding of oligomeric proteins with folded monomeric intermediates. The effect of dilution of the protein and ligation by up to two different types of ligands at multiple binding sites upon the dissociation and unfolding properties of the oligomers is now possible. The second advance which has been incorporated into the modeling capabilities of the BIOEQS program is the option of considering perturbations to the multiple binding or folding equilibria by chemical denaturants, temperature, or high hydrostatic pressure. Additional improvements to the BIOEQS program include direct mapping of individual species or sums of species to the numerical physical experimental observable. The values of the observable corresponding to particular species or to 0 and 100% completion of a titration can be either fixed or floating parameters in the fit.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed1992

Identification of actin and HSP 70 as cyclosporin A binding proteins by photoaffinity labeling and fluorescence displacement assays.

A novel family of cyclosporin A (CsA) binding proteins was identified by using the biologically active, radioiodinated photoaffinity probe [D-Lys-N epsilon-(4-azido-3-[125I]iodophenyl)propionyl)]8-CsA. In addition to cyclophilin, proteins with molecular masses of 43 kDa and approximately 50-55 kDa were labeled in Jurkat extracts and bovine calf thymus. Sequence analysis of the 43-kDa protein purified from calf thymus and subsequent Western analysis of CsA affinity-purified material from Jurkat extracts identified the 43-kDa component as actin. [D-Lys-N epsilon-(5-dimethylamino-1-naphthalenesulfonyl)]8-CsA, a fluorescent analogue of CsA, was prepared and used to measure the binding constants of cyclosporin derivatives to actin by means of a new fluorescence displacement assay. [D-Lys-N epsilon-(5-dimethylamino-1-naphthalenesulfonyl)]8-CsA and [N delta-t-butoxycarbonyl diaminobutyryl)]8-CsA bind to bovine actin at physiologically relevant concentrations, with dissociation constants of 60 +/- 33 and 570 +/- 380 nM, respectively. Because the ATPase fragment of heat shock cognate 70 (HSC 70) is structurally related to actin, the yeast homologue SSA1 was tested and found to be radiolabeled by the cyclosporin A photoaffinity reagent. The binding constant for [D-Lys-N epsilon-(5-dimethylamino-1-naphthalenesulfonyl)]8-CsA to SSA1 was determined and is 53 +/- 48 nM. These results indicate that actin and the 70-kDa heat shock protein family contain a structurally related domain for binding of cyclosporin A-related peptides.

Actins↗
PubMed1992

Unfolding of trp repressor studied using fluorescence spectroscopic techniques.

The unfolding properties of the trp repressor of Escherichia coli have been studied using a number of different time-resolved and steady-state fluorescence approaches. Denaturation by urea was monitored by the average fluorescence emission energy of the intrinsic tryptophan residues of the repressor. These data were consistent with a two-state transition from dimer to unfolded monomer with a free energy of unfolding of 19.2 kcal/mol. The frequency response profiles of the fluorescence emission brought to light subtle urea-induced modifications of the intrinsic tryptophan decay parameters both preceding and following the main unfolding transition. The increase of lifetime induced by urea required higher concentrations of urea than the increase in the total intensity described by Gittelman and Matthews [(1990) Biochemistry 29, 7011]. This indicates that the intensity increase has both dynamic and static origins. To assess the effect of tryptophan binding upon repressor stability, and to determine whether repressor oligomerization would be detectable in an unfolding experiment, we examined denaturation profiles of repressor labeled with the long-lived fluorescence probe 5-(dimethylamino)naphthalene-1-sulfonyl (DNS), by monitoring the average rotational correlation time of the probe. These experiments revealed a protein concentration dependent transition at low urea concentrations. This transition was promoted by tryptophan binding. We ascribe this transition to urea-induced dissociation of repressor tetramers. The main unfolding transition of the dimer to unfolded monomer was also observable using this technique, and the free energies associated with this transition were 18.3 kcal/mol in the absence of tryptophan and 24.1 kcal/mol in its presence, demonstrating that co-repressor binding stabilizes the repressor dimer against denaturation.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Proteins↗
PubMed1992

Solution studies of the interactions between the histone core proteins and DNA using fluorescence spectroscopy.

The equilibrium interactions between histone H2A-H2B and H3/H4 subunits with 200 base pair chicken erythrocyte DNA have been studied by monitoring the fluorescence polarization of a long-lived fluorescence probe covalently bound to the histone subunits. These studies have brought to light the formation of highly asymmetric complexes exhibiting very high histone/DNA stoichiometries as well as very high apparent affinities. The stoichiometries observed for these non-nucleosome complexes depended both upon the concentration of the histones and the concentration of the DNA 200mer. The observed stoichiometries varied approximately between 4 and 16 histone octamers/DNA 200mer and the affinities were in the nanomolar range. These results are discussed in terms of their in vitro as well as their possible in vivo significance.

Animals↗
PubMed1992

Investigation of the structural determinants of the intrinsic fluorescence emission of the trp repressor using single tryptophan mutants.

The fluorescence decay properties of wild-type trp repressor (TR) have been characterized by carrying out a multi-emission wavelength study of the frequency response profiles. The decay is best analyzed in terms of a single exponential decay near 0.5 ns and a distribution of lifetimes centered near 3-4 ns. By comparing the recovered decay associated spectra and lifetime values with the structure of the repressor, tentative assignments of the two decay components recovered from the analysis to the two tryptophan residues, W19 and W99, of the protein have been made. These assignments consist of linking the short, red emitting component to emission from W99 and most of the longer bluer emitting lifetime distribution to emission from W19. Next, single tryptophan mutants of the repressor in which one of each of the tryptophan residues was substituted by phenylalanine were used to confirm the preliminary assignments, inasmuch as the 0.5-ns component is clearly due to emission from tryptophan 99, and much of the decay responsible for the recovered distribution emanates from tryptophan 19. The data demonstrate, however, that the decay of the wild-type protein is not completely resolvable due both to the large number of components in the wild-type emission (at least five) as well as to the fact that three of the five lifetime components are very close in value. The fluorescence decay of the wild-type decay is well described as a combination of the components found in each of the mutants. However, whereas the linear combination analysis of the 15 data sets (5 from the wild-type and each mutant) yields a good fit for the components recovered previously for the two mutants, the amplitudes of these components in the wild-type are not recovered in the expected ratios. Because of the dominance of the blue shifted emission in the wild-type protein, it is most likely that subtle structural differences in the wild-type as compared with the mutants, rather than energy transfer from tryptophan 19 to 99, are responsible for this failure of the linear combination hypothesis.

Bacterial Proteins↗
PubMed1990

Subunit interactions in hemoglobin probed by fluorescence and high-pressure techniques.

The dissociation of the subunits of human adult oxyhemoglobin has been investigated by using steady-state fluorescence anisotropy, multifrequency phase fluorometry, and high hydrostatic pressure. Human hemoglobin obtained by using two purification procedures (bulk preparation by centrifugation or further fractionation using anion-exchange chromatography) was labeled with an extrinsic fluorescent probe, 5-(dimethylamino)naphthalene-1-sulfonyl chloride (DNS-Cl). The long fluorescence lifetime of this probe allows for the observation of the macromolecular tumbling, and thus provides a method for observing changes in the size of the complex upon subunit dissociation under differing solution conditions of proton and organic phosphate concentration. At pH 7, the dansylated preparations of bulk and fractionated hemoglobin showed a concentration-dependent decrease in the anisotropy which though not identical can only arise from the tetramer to dimer dissociation. We observed primarily the dimer at pH 9 and a small destabilization of the tetramer in the presence of saturating inositol hexaphosphate (IHP). High-pressure experiments allowed for the observation of the dissociation of the hemoglobin dimer into monomers. From these measurements, we estimate the dimer dissociation constant to be between 0.1 and 1 nM. We compare the present results on the subunit affinities in hemoglobin obtained from steady-state and time-resolved fluorescence data with those obtained previously by using gel filtration, sedimentation, and kinetic techniques. These comparisons are indicative of a certain degree of conformational heterogeneity in the hemoglobin preparations.

Chromatography, Gel↗
PubMed1990

Macromolecular binding equilibria in the lac repressor system: studies using high-pressure fluorescence spectroscopy.

High hydrostatic pressure coupled with fluorescence polarization has been used to investigate protein subunit interactions and protein-operator association in lac repressor labeled with a long-lived fluorescent probe. On the basis of observation of a concentration-dependent sigmoidal decrease in the dansyl fluorescence polarization, we conclude that application of high hydrostatic pressure results in dissociation of the lac repressor tetramer. The 2-fold decrease in the rotational relaxation time and the high-pressure plateau are consistent with a tetramer to dimer transition. The volume change for tetramer dissociation to dimer is -82 +/- 5 mL/mol. The dissociation constant calculated from the data taken at 4.5 degrees C is 4.3 +/- 1.3 nM. The tetramer dissociation constant increases by a factor of 3 when the temperature is raised from 4.5 to 21 degrees C. A very small effect of inducer binding on the subunit dissociation is observed at 4.5 degrees C; the Kd increases from 4.5 to 7.1 nM. At 21 degrees C, however, inducer binding stabilizes the tetramer by approximately 0.8 kcal/mol. Pressure-induced monomer formation is indicated by the curves obtained upon raising the pH to 9.2. The addition of IPTG shifts the pressure transition to only slightly higher pressures at this pH, indicating that the stabilization of the tetramer by inducer is not as marked as that observed at pH 7.1. From the decrease in the polarization of the dansyl repressor-operator complexes, we also conclude that the application of pressure results their dissociation and that the volume change is large in absolute value (approximately 200 mL/mol). The lac repressor-operator complex is more readily dissociated upon the application of pressure than the tetramer alone, indicating that operator binding destabilizes the lac repressor tetramer.

Dansyl Compounds↗
PubMed1990

Analysis of binding in macromolecular complexes: a generalized numerical approach.

In this work, we introduce a generalized, global numerical methodology for analysis of binding phenomena in complex macromolecular assemblies. On the basis of a numerical algorithm (EQS) to solve systems of simultaneous free energy equations, binding profiles of simple to highly complex interacting systems can be analyzed over any concentration region without any need to generate an analytical form to describe the data. The output of the numerical algorithm is the concentration of each individual species in solution, allowing the generation of all possible binding profiles of the system (e.g., protein saturation by ligand). We present here the application of this approach to the DNA-protein subunit-ligand interactions of the trp repressor system as a typical example. From a practical point of view, the analysis program is capable of the rapid and simultaneous analysis of multiple binding profiles in terms of internally consistent sets of free energies. Given both the enormous complexity, as well as the underlying subtlety, involved in the regulation of biological function, the present generalized approach to analyzing macromolecular binding should find wide applications.

Algorithms↗
PubMed1990

Resolution of the fluorescence decay of the two tryptophan residues of lac repressor using single tryptophan mutants.

We have studied the time-resolved intrinsic tryptophan fluorescence of the lac repressor (a symmetric tetramer containing two tryptophan residues per monomer) and two single-tryptophan mutant repressors obtained by site-directed mutagenesis, lac W201Y and lac W220Y. These mutant repressor proteins have tyrosine substituted for tryptophan at positions 201 and 220, respectively, leaving a single tryptophan residue per monomeric subunit at position 220 for the W201Y mutant and at position 201 in the W220Y mutant. It was found that the two decay rates recovered from the analysis of the wild type data do not correspond to the rates recovered from the analysis of the decays of the mutant proteins. Each of these residues in the mutant repressors displays at least two decay rates. Global analysis of the multiwavelength data from all three proteins, however, yielded results consistent with the fluorescence decay of the wild type lac repressor corresponding simply to the weighted linear combination of the decays from the mutant proteins. The effect of ligation by the antagonistic ligands, inducer and operator DNA, was similar for all three proteins. The binding of the inducer sugar resulted in a quenching of the long-lived species, while binding by the operator decreased the lifetime of the short components. Investigation of the time-resolved anisotropy of the intrinsic tryptophan fluorescence in these three proteins revealed that the depolarization of fluorescence resulted from a fast motion and the global tumbling of the macromolecule. Results from the simultaneous global analysis of the frequency domain data sets from the three proteins revealed anisotropic rotations for the macromolecule, consistent with the known elongated shape of the repressor tetramer. In addition, it appears that the excited-state dipole of tryptophan 220 is alighed with the long axis of the repressor.

Ligands↗
PubMed1989

Salt effects on histone subunit interactions as studied by fluorescence spectroscopy.

The salt concentration dependence of the aggregation properties of calf thymus and chicken erythrocyte histones has been investigated by using fluorescence spectroscopy. The isolated H2A/H2B and H3/H4 subunit preparations were labeled with 5-(dimethylamino)naphthalene-1- sulfonyl (dansyl). This long-lived fluorescence probe allows for the observation of rotations due to tumbling of the particle and thus is a probe for changes in the size of macromolecular assemblies. The fluorescence polarization and lifetime were measured as a function of salt concentration for these isolated preparations. Next, each labeled preparation was reconstituted with its unlabeled complement, and the salt concentration dependence of histone core octamer interactions was investigated in the same manner. Salt-induced core particle formation was observed by monitoring the dansyl-labeled dimers for both the calf thymus and chicken erythrocyte preparations. Evidence for subunit dissociation of the isolated H2A-H2B preparations was also found, as well as aggregation of the isolated H3/H4 subunits to at least dimers of tetramers. The calf thymus H3/H4 preparation was in aggregated form under all conditions studied, whereas the chicken erythrocyte H3/H4 only formed aggregates at high protein or salt concentrations. We have found evidence that the dimer can displace the tetramer from the higher order aggregate in order to form core particles. Such competition between the subunit interfaces in the histone system suggests that they may play a regulatory role in histone-DNA interactions.

Animals↗
PubMed1989

Histone subunit interactions as investigated by high pressure.

High-pressure fluorescence polarization was used to investigate subunit interactions of the histone H2A-H2B dimer and the H3/H4 tetramer isolated from calf thymus (CT) and chicken erythrocyte (CE) chromatin. The proteins were individually labeled with the fluorescent probe 5-(dimethylamino)-naphthalene-1-sulfonate (dansyl or DNS), and the fluorescence polarization was measured as a function of pressure. The long fluorescence lifetime of the probe allows for the observation of global rotations of the protein, the rate of which is dependent upon the aggregation state. From the pressure dependence of the dansyl polarization, the Kd of H2A-H2B dissociation of the CE dimer was found to be approximately 1 X 10(-7) M at 2.0 M NaCl. Lowering the salt concentration to 200 mM slightly stabilized the protein to 6 X 10(-8) M. Our data indicate a small negative volume change for the dissociation of the core particle octamer. The (H3)2(H4)2 tetramer, as was shown in the previous paper (Royer et al., 1989), also formed predominantly dimers of tetramers at higher protein or salt concentrations. In the study presented here, we found the dissociation constant for the H3/H4 octamer to dimer transition to be 1 X 10(-21) M3 (C1/2 = 4 X 10(-8) M) at 2 M NaCl for the CT preparation. Decreasing the salt concentration to 200 mM reduced the stability of the CT H3/H4 octamer to 9 X 10(-21) M3 (C1/2 = 8 X 10(-8) M). The dimer of the CE tetramer also dissociated upon application of pressure in 2 M salt.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗