Synthesis of a protein-reactive ATP analog and its application for the affinity labeling of rabbit-muscle actin

Covalent binding of ATPgammaS to the nucleotide-binding site in S14C-actin

We have recently reported on the characterization of beta-actin carrying the mutation S14C in one of the phosphate-binding loops. The present paper describes the attachment of the adenosine 5'-[gamma-thio]-triphosphate (ATPgammaS) to actin containing this mutation. Treatment of S14C-actin with ATPgammaS blocked further nucleotide exchange and raised the thermal stability of the protein, suggesting the formation of a covalent bond between the sulfhydryl on the terminal phosphate of ATPgammaS and cysteine-14 of the mutant actin. The affinity of the derivatized G-actin for DNase I as compared to wild-type ATP-actin was lowered to a similar extent as that of ADP.AlF(4)-actin. The derivatized actin polymerized slower than ATP-actin but faster than ADP-actin. Under these conditions the bound ATPgammaS was hydrolyzed, suggesting the formation of a state corresponding to the transient ADP.P(i)-state. ATPgammaS-actin interacted normally with profilin, whereas the interaction with actin depolymerizing factor (ADF) was disturbed, as judged on the effects of these proteins on actin polymerization.

Cross-linking of nucleic acids to proteins. Modified poly(A) as mRNA for Escherichia coli ribosomes

Poly(adenylic acid) was modified by methylchlorotetrolic ester in a reproducible and defined content of the derivatized bases. The nucleic acid derivative is protein reactive and was coupled to 70S ribosomes from Escherichia coli, in order to identify proteins along the mRNA pathway. The binding of the label becomes specific under the direction of tRNA(Lys) and is then almost exclusively located on the small subunit. The proteins S1, S12, S18 and S21 were labeled, as shown by an antibody assay. The yield of the affinity label was 5.4%, as calculated from the labeled nucleic acid. This compares favourably with the yields from photolabile compounds.

Substoichiometric concentrations of ATP-G-actin are required to anneal actin polymerized by calcium ions

At 3 degrees C and pH 7.0, the addition of 40 nM ATP-G-actin to F-actin (12 microM as the monomer), polymerized in the presence of 4 mM CaCl2, determines a substantial and rapid increase of the viscosity of the solution, which is accompanied by the incorporation of the ATP-G-actin added into the polymer. The hypothesis that the presence of ATP-actin at the filament end(s) promotes the annealing reaction is substantiated by the finding that, after the addition of ATP-G-actin, the average filament length is increased. This finding is relevant, not only because it provides evidences in favour of the existence of annealing but also because it shows that the concentration of ATP-G-actin influences the filaments length distribution through a mechanism different from the elongation reaction.

Evidence for direct binding of vinculin to actin filaments

The interaction of vinculin with actin filaments was investigated by methods which exclude interference by contaminating proteins which may occur in vinculin preparations. Vinculin which was blotted from SDS-polyacrylamide gels onto nitrocellulose, was stained specifically by fluorescently labeled polymeric actin (100 mM KCl, 2 mM MgCl2). Vinculin which was purified from alpha-actinin and an actin polymerization-inhibiting protein (HA1), was found to be cosedimented with polymeric actin. Maximally one vinculin molecule was cosedimented per one hundred actin filament subunits. Half maximal binding of vinculin was observed at about 0.25 microM free vinculin. Vinculin could be replaced from actin by the addition of tropomyosin.

pH-dependent rate of formation of the gelsolin-actin complex from gelsolin and monomeric actin

The assembly of gelsolin with actin was followed by the increase of the fluorescence intensity of a fluorescence label bound to actin. The time course of the formation of the gelsolin-actin complex in the presence of micromolar [Ca2+] could be quantitatively interpreted by a model in which one actin molecule binds slowly to gelsolin in a rate-determining step and subsequently a second actin molecule is bound at least 40 times more rapidly. The rate of binding of the first actin molecule to gelsolin was found to be remarkably slow and to depend on the pH. The rate constants of formation of the gelsolin-actin complex range from 1.5 X 10(4) M-1 s-1 at pH 8 to 7 X 10(4) M-1 s-1 at pH 6.

Binding of phosphate ions to actin

The decrease of the critical monomer concentration of ADP-actin by millimolar phosphate concentrations has been analysed in terms of equilibrium constants for binding of phosphate ions to ADP-actin. The decrease has been explained by a 10-fold greater affinity of phosphate ions to polymeric ADP-actin (binding constant 100 M-1) than to monomeric ADP-actin (binding constant 10 M-1). Phosphate has an almost identical effect on the critical monomer concentration of the pointed ends of gelsolin-capped actin filaments in the presence of ATP. The phosphate concentration required for half-maximal decrease of the critical monomer concentration of the pointed ends has been determined to be about 15 mM. By using the fluorescent ATP-analogue, 1,N6-ethenoadenosine 5'-triphosphate, phosphate ions have been found to bind also to monomeric ATP-actin, yet with a slightly higher affinity than to monomeric ADP-actin (binding constant 50 M-1).

Fluorescence energy transfer between points in G-actin: the nucleotide-binding site, the metal-binding site and Cys-373 residue

Fluorescence energy transfers were studied in order to investigate the spatial relationships between the nucleotide-binding site, the metal-binding site and the Cys-373 residue in the G-actin molecule. When 1-N6-ethenoadenosine-5'-triphosphate (epsilon-ATP) in the nucleotide-binding site and Co2+ or Ni2+ in the metal-binding site were used as fluorescence donor and acceptor, respectively, the fluorescence intensity of epsilon-ATP was perfectly quenched by Ni2+ or Co2+. This indicated that the nucleotide-binding site is very close to the metal-binding site; the distance should be less than 10 A. When N-iodoacetyl-N'-(5-sulfo-1-naphthyl)ethylenediamine (IAEDANS) bound to Cys-373 residue and Co2+ in the metal-binding site were used as a fluorescence donor and an acceptor, respectively, the transfer efficiency was equal to 5 +/- 1%. The corresponding distance was calculated to be 23-32 A, assuming a random orientation factor K2 = 2/3.

Functionality of muscle proteins in gelation mechanisms of structured meat products

Recent advances in muscle biology concerning the discoveries of a large variety of proteins have been described in this review. The existence of polymorphism in several muscle proteins is now well established. Various isoforms of myosin not only account for the difference in physiological functions and biochemical activity of different fiber types or muscles, but also seem to differ in functional properties in food systems. The functionality of various muscle proteins, especially myosin and actin in the gelation process in modal systems which simulate structured meat products, is discussed at length. Besides, the role of different subunits and subfragments of myosin molecule in the gelation mechanism, and the various factors affecting heat-induced gelation of actomyosin in modal systems are also highlighted. Finally, the areas which need further investigation in this discipline have been suggested.

Fluorescence energy transfers between points in acto-subfragment-1 rigor complex

Fluorescence energy transfer was measured by time-resolved and steady-state fluorimetry in order to investigate the spatial relationships between the nucleotide binding site of actin, the Cys-373 residue of actin, and the SH1 of myosin subfragment-1 in the rigor complex of acto-subfragment-1. N-Iodoacetyl-N'-(5-sulfo-1-naphthyl)ethylenediamine (IAEDANS) bound to the Cys-373 of actin or the fluorescent ADP analogue 1-N6-ethenoadenosine-5'-diphosphate (epsilon-ADP) bound to F-actin was used as a donor and 4-(N-(iodoacetoxy)ethyl-N-methyl)amino-7-nitrobenz-2-oxa-1,3-diazo le (IANBD) or 5-iodoacetamidofluorescein (IAF) bound to SH1 of myosin subfragment-1 was used as an acceptor. Assuming the random orientation factor, K2, to be 2/3, the distance between Cys-373 residue of actin and SH1 of myosin subfragment-1 was calculated to be about 50 A, in agreement with the values previously reported, 60 A (Takashi, R. (1969) Biochemistry 18, 5164-69) and 50 A (Trayer, H.R. and Trayer, I.P. (1983) Eur. J. Biochem. 135, 47-59). The distance between the nucleotide binding site of actin and SH1 of myosin subfragment-1 was calculated to be about 70 A or greater.

Similar affinities of ADP and ATP for G-actin at physiological salt concentrations

The equilibrium constant for the exchange of ATP and ADP at G-actin was determined by fluorimetric titration of G-actin-bound epsilon-ATP by ATP or ADP. The affinity of ATP for G-actin was found to be only about 3-fold higher than the affinity of ADP for G-actin at 37 degrees C, pH 7.5 and physiologically relevant salt concentrations (100 mmol K+/l, 0.8 mmol Mg2+/l, less than 0.01 mmol Ca2+/l).

Possible involvement of a calmodulin regulated Ca2+ -ATPase in exocytosis performance in Paramecium tetraurelia cells

Surface membrane fractions from Paramecium tetraurelia cells contain a calmodulin-stimulated Ca2+-ATPase responding to low levels of free Ca2+ and with features characteristic of a membrane-bound ATPase. Among the different strains analyzed this enzyme was practically absent selectively from the 'non-discharge' mutant nd9-28 degrees C (from J. Beisson): if cultured at a permissive temperature (18 degrees C), this strain showed identical values of calmodulin-stimulated Ca2+-ATPase activity as wild-type cells (7S) or strains with mutations which do not affect exocytosis performance. We conclude that this calmodulin-stimulated Ca2+-activated ATPase might be a prerequisite for membrane fusion in the course of exocytosis performance.

Characterization of an ATPase on the inside of rat-liver nuclear envelopes by affinity labeling

Nuclear envelope membranes from rat liver cells contain ATPases, one of which can be inhibited and irreversibly labeled by (S-dinitrophenyl)-6-mercaptopurine riboside triphosphate. Inhibition and covalent substitution of the ATPase are achieved only after disruption of the nuclei, the ATP analogue is inactive on the ATPase activity of whole nuclei or on vesicles of the membrane prepared after a modified heparin method of Bornens and Courvalin. Electron micrographs and scanning micrographs helped to establish the characterization of closed vesicles and intact nuclei. With the aid of (alpha-32P)-labeled, and of the (beta, gamma-32P)-labeled analogue, it was possible to demonstrate the incorporation of the nucleotide into a few protein regions of the nuclear membrane disc electrophoresis pattern.

Multiple supramolecular structures formed by interaction of actin with protamine

When protamine is added to actin, different supramolecular structures are formed depending on the molar ratio of the two proteins and of the ionic strength of the medium. At low ionic strength, and going from a molar ratio of protamine to G-actin of 4:1, 2:1 and 1:1, globular aggregates are first converted into extended structures and then to long threads in which the constituent ATP-G-actin is rapidly exchangeable with the actin of the medium. At high ionic strength {Tyrode [(1910) Arch. Int. Pharmacodyn. Ther.20, 205-212] solution}, starting from G-actin and protamine in the 1:1 molar ratio, long ropes are formed that can be resolved into intertwining filaments of 4-5nm diameter. The addition of protamine in a 1:1 molar ratio to a solution of F-actin in Tyrode solution causes the breakage of the actin filaments, which is also revealed by the decrease of the viscosity of the solution and the formation of ordered latero-lateral aggregates. The structures formed by reaction of protamine with G-actin can be separated from free G-actin and protamine by filtration through 0.45mum-pore-size Millipore filters. This technique has been exploited to study the exchange reaction between free actin and the actin-protamine complexes. For these studies the 1:1 actin-protamine complex formed at low ionic strength and the 2:1 actin-protamine complex formed in the presence of 23nm-free Mg(2+) have been selected. In the first case the exchange reaction is practically complete in the dead time of the experiment (20s). In the second case, where the complex operates like a true ATPase, the rate of the exchange is initially comparable with the rate of the ATP cleavage. Later on, however, the complex undergoes a change and the rate of the exchange between free actin and the actin bound to protamine becomes lower than the rate of the ATPase reaction. It is proposed that the ATP exchanges for ADP directly on the G-actin bound in the complex.

Dynamic aspects of structural proteins in vertebrate skeletal muscle

In this review, our current knowledge on the structural proteins of vertebrate skeletal muscle is briefly outlined. Structural proteins include the contractile proteins (actin and myosin), the major regulatory proteins (troponin and tropomyosin), the minor regulatory proteins (M-protein, C-protein, F-protein, I-protein, and actinins), and the scaffold proteins (connectin, desmin, and Z-protein). In addition, the relative turnover rates of the muscle proteins (M-protein greater than or equal to troponin greater than soluble protein as a whole greater than tropomyosin not equal to alpha-actinin greater than myosin greater than 10S-actinin greater than actin) are discussed. The changes in the turnover of muscle proteins are compared in denervated and dystrophic muscles. The properties of the various proteases in muscle, including alkaline protease, calcium-activated neutral protease (CANP), and acidic protease (cathepsins), and the structural alterations of myofibrils by these proteases are also described. Finally, the role of proteases and their inhibitors in diseased muscle is summarized, with focus on CANP and its inhibitors, leupeptin and E-64.

Fluorescence energy transfer between epsilon-ATP at the nucleotide binding site and N-(4-dimethylamino-3,5-dinitrophenyl)-maleimide at Cys-373 of G-actin

The method of fluorescence energy transfer is used to measure the distance from the nucleotide binding site to Cys-373 of G-actin. The fluorescent ATP analogue 1-N6-ethenoadenosine 5'-triphosphate was used as donor and N-(4-dimethylamino-3,5-dinitrophenyl)-maleimide was used as acceptor. From the measurements of the efficiency of fluorescence energy transfer by both static and time resolved fluorometries, the distance between nucleotide binding site and Cys-373 residue of G-actin was calculated to be about 30 A.

The polymerization reaction of muscle actin

Recent advances in the studies of the aggregation of G-actin monomers, containing one molecule of ATP, to long filaments of F-actin, with a concomitant hydrolysis of the nucleotide to ADP, are reviewed. With the aid of omega-ATP, the association and dissociation rate constant of the nucleotide could be determined. The binding of the nucleotide is enhanced by the binding of one Ca++ ion, probably at a different site. The delta G value of the Mg++ or Ca++ induced polymerization has been determined to --39 to--59 kJ/mole, the critical protein concentration for the ATP-G-actin to ADP-F-actin conversion is very strongly influenced by the concentration of bivalent cations. The rate constants of the protein monomers, and the rate and equilibrium constants for the propagation step show the process to be extremely cooperative. Actin shows the interesting phenomenon of translocational head-to-tail polymerization, which may be regulated by ATP. The contact sites between the monomers in F-actin have been labeled by chemical modification. Two tryosine residues, 53 and 69, are probably close to one of the two sites. The ATP binding sites has been labeled by an ATP analog, and there is evidence that it is close to the contact site.

Affinity labeling of rabbit muscle pyruvate kinase by 5'-p-fluorosulfonylbenzoyladenosine

Rabbit muscle pyruvate kinase is irreversibly inactivated upon incubation with the adenine nucleotide analogue, 5'-p-fluorosulfonylbenzoyladenosine. A plot of the time dependence of the logarithm of the enzymatic activity at a given time divided by the initial enzymatic activity(logE/Eo) reveals a biphasic rate of inactivation, which is consistent with a rapid reaction to form partially active enzyme having 54% of the original activity, followed by a slower reaction to yield totally inert enzyme. In addition to the pyruvate kinase activity of the enzyme, modification with 5'-p-fluorosulfonylbenzoyladenosine also disrupts its ability to catalyze the decarboxylation of oxaloacetate and the ATP-dependent enolization of pyruvate. In correspondence with the time dependence of inactivation, the rate of incorporation of 5'-p-[14C]fluorosulfonylbenzoyladenosine is also biphasic. Two moles of reagent per mole of enzyme subunit are bound when the enzyme is completely inactive. The pseudo-first-order rate constant for the rapid rate is linearly dependent on reagent concentration, whereas the constant for the slow rate exhibits saturation kinetics, suggesting that the reagent binds reversibly to the second site prior to modification. The adenosine moiety is essential for the effectiveness of 5'-p-fluorosulfonylbenzoyladenosine, since p-fluorosulfonylbenzoic acid does not inactivate pyruvate kinase at a significant rate. Thus, the reaction of 5'-p-fluorosulfonylbenzoyladenosine with pyruvate kinase exhibits several of the characteristics of affinity labeling of the enzyme. Protection against inactivation by 5'-p-fluorosulfonylbenzoyladenosine is provided by the addition to the incubation mixture of phosphoenolpyruvate. Mg-ADP or Mg2+. In contrast, the addition of pyruvate, Mg-ATP, or ADP and ATP alone has no effect on the rate of inactivation. These observations are consistent with the postulate that the 5'-p-fluorosulfonylbenzoyladenosine specifically labels amino acid residues in the binding region of Mg2+ and the phosphoryl group of phosphoenolpyruvate which is transferred during the catalytic reaction. The rate of inactivation increases with increasing pH, and k1 depends on the unprotonated form of an amino acid residue with pK = 8.5. On the basis of the pH dependence of the reaction of pyruvate kinase with 5'-p-fluorosulfonylbenzoyladenosine and the elimination of cysteine residues as possible sites of reaction, it is postulated that lysyl or tyrosyl residues are the most probably candidates for the critical amino acids.

Membrane-bound F1 ATPase from Micrococcus Sp. ATCC 398E. Purificationa and characterization ny affinity chromatography

A chemically reactive ATP analogue, 6-[(3-carboxy-4-nitrophenyl)thio]-9-beta-D-ribofuranosylpurine 5'-triphosphate (Nbs6ITP) has been synthesized. It has the ability to form stable thioether bonds between the 6-position of the purine ring and aliphatic mercapto groups. The nucleotide moiety of the reagent has been covalently bound to agarose, via iminobispropylamine and N-acetyl-homocysteine as space with the purpose of producing an affinity chromatography material. The affinity matrix binds solubilized F1 ATPase from a crude extract of Micrococcus sp. membranes. Afterwards the enzyme can be selectively eluted from the column at a defined ATP concentration. This method is superior to the conventional purification with respect to speed and convenince of the preparation. The affinity chromatography leads in a one-step process to the same purity to enzyme, substituting several steps of the conventional method. In addition, the affinity matrix was used for binding studies. Although the presence of Mg2+ ions is a prerequisite for the hydrolysis of nucleoside 5'-triphosphates, evidence is presented indicating that the binding of the nucleoside triphosphates to highly purified F1 ATPase from Micrococcus sp. appears not to be influenced by Mg2+ ion concentrations so far examined.

Fluorescent guanosine-nucleotide analogs suitable for photoaffinity-labeling experiments

The synthesis and properties of strongly fluorescent derivative of inosine and its nucleotides are described. Reaction of 2-chloro-inosinic acid with sodium azide leads to a product bearing the tetrazole ring between position 2 and 3. Methylation at N1 was effected with dimethyl sulfate. The corresponding nucleosides and their 5'-triphosphates were also prepared. Only the non-methylated series is at equilibrium with small concentrations of their azido forms, and can be photolyzed by wavelengths above 300 nm. Both series are strongly fluorescent, their emission and excitation fluorescence spectra, as well as their quantum yields were measured. The nucleoside 5'-triphosphates are able to initiate and sustain polymerization of porcine brain tubulin.

Kinetic analysis of ATPase mechanisms

At even the simplest level we can expect an ATPase mechanism to comprise the following four steps: the binding of ATP, the reaction of ATP with water on the enzyme, and the release of the products ADP and P1. So at the outset techniques are needed to investigate these four processes. The range of techniques needed is soon extended once questions are asked about the role of protons and metal ions, the possibility of a multistep hydrolytic process, multistep substrate and product binding processes, and protein–lipid or protein–protein interactions. Since ATPases and ATP synthases are almost universally involved in some form of energy transduction there is a particular need in an ATPase or ATP synthase reaction to evaluate the equilibrium constants of the steps in the mechanism and to investigate the possibility of alternate reaction pathways. The nature of the coupling process by the protein of the chemical reactions of ATP to the other energetic process, be it muscle contraction, active transport, respiration or photosynthesis, is likewise of profound interest. Finally we would like to know as much as possible about the ATPase or ATP synthase mechanism during the period when the various forms of energy transduction are occurring.

Affinity labelling to - SH groups in adenosine - triphosphate - phosphoribosyl transferase with the dinitrophenyl group from S-dinitrophenyl-6-mercaptopurine-riboside 5'-phosphate

Adenosine-triphosphate-phosphoribosyl transferase from Escherichia coli reacts with S-dinitrophenyl-6-mercaptopurine-riboside 5'-phosphate. In this reaction the dinitrophenyl group becomes attached to the enzyme, while the nucleotide is split off. Most aliphatic high and low-molecular-weight-SH compounds react with the thioether in the opposite way, i.e. bind the nucleotide and split off dinitrothiophenol. It appears that the dinitrophenyl moiety of the thioether interacts with the enzyme in a specific way, and that this interaction activates the bond between the dinitrophenyl group and the sulfur atom. In support of this it was found that dinitrophenol inhibits the transferase reaction with half maximal effect at 0.4 mM. The inhibition is competitive with ATP. Dinitrophenol also competes with ATP in binding studies.

The kinetics of the exchange of G-actin-bound 1: N6-ethenoadenosine 5'-triphosphate with ATP as followed by fluorescence

1: N6-Ethenoadenosine 5'-triphosphate (epsilonATP), a fluorescent analog of ATP, binds to monomeric actin with a binding constant which is only about 5 times smaller than that of ATP. The spectroscopic changes which occur when epsilonATP binds to actin are studied and used to monitor the kinetics of nucleotide exchange. The first-order rate constant which is measured at a large excess of ATP over epsilonATP strongly depends on the ATP and Ca+ concentrations. This finding is explained by a mechanism in which the nucleotide dissociates much more easily from Ca2+-free than from Ca2+-bound actin. Of special interest is the temperature dependence of the dissociation rate constant. The Arrhenius plot shows a sharp bend near 24 degrees C.

The role of the bound nucleotide in the polymerization of actin

Three mucleotides, ATP, ADP, and an unsplit-table analog of ATP (adenylyl imidodiphosphate (AMPPNP)), were bound to monomeric actin, and their effects on the rate and extent of the actin polymerization were studied. The kinetics of polymerization, assayed by the change in OD232, followed a simple exponential curve. The rates of polymerization were equal for bound ATP and AMPPNP; both of which were three to five times faster than the rate for ADP. The concentration of actin monomers in apparent equilibrium with the polymer, G(180 degrees longitude), was determined. Values of G(180 degrees longitude) in 100 mM KCl were found for different nucleotides to be: G-ATP(180 degrees longitude) = 0.7 mu-M, G-AMPPNP(180 degrees longitude) = 0.8 MU-M, and G-ADP(180 degrees longitude) = 3.4 mu-M. The equilibrium constant of the polymerization is given by K = [G(180 degrees longitude)]-minus 1 when no nucleotide is split. The polymerization of actin-ATP is more complex due to the splitting of the nucleotide and our data require that this polymerization involves more than one step. The kinetic parameters for the polymerization of actin-ATP can be explained by a simple scheme in which the nucleotide dephosphorylation occurs in a step following the polymerization step. The conclusions are: (1) the binding of ATP to actin monomer promotes polymerization slightly more than the binding of ADP, (2) actin bound ATP provides less than 4 kJ/mol of free energy to promote polymerization, and (3) the dephosphorylation of the nucleotide is not coupled to polymerization.