Anomalous fluorescence of yeast 3-phosphoglucerate kinase

Quenching of the fluorescence of Tyr and Trp residues of firefly luciferase from Luciola mingrelica by the substrates

Luciferase of the firefly Luciola mingrelica is characterized by fluorescence of not only the unique Trp residue (lambda(em) = 340 nm), but also that of Tyr residues (lambda(em) = 308 nm). Quenching of the intrinsic fluorescence of the luciferase by its substrates luciferin and ATP (AMP) has been studied. Luciferin (LH2) quenches Trp fluorescence more efficiently than the fluorescence of Tyr residues. Two centers of quenching of Tyr fluorescence by ATP have been found corresponding apparently to the allosteric and active sites of the luciferase with K(s(ATP)) = 20 and 110 microM, respectively. The influence of one substrate on the affinity of luciferase to the second was investigated using fluorescence. ATP (AMP) binding to the allosteric sites of the luciferase significantly affects the affinity of luciferase to LH2. Formation of the complex between the luciferase and LH2 affects the affinity of both allosteric and active sites of the luciferase to ATP (AMP). The observed effects are probably connected with conformational changes in the luciferase molecule upon its interaction with the substrates.

Steady-State Kinetics and Tryptophan Fluorescence Properties of Halohydrin Dehalogenase from Agrobacterium radiobacter. Roles of W139 and W249 in the Active Site and Halide-Induced Conformational Change

Halohydrin dehalogenase (HheC) from Agrobacterium radiobacter AD1 is a homotetrameric protein containing four tryptophan residues per subunit. The fluorescence properties of the enzyme are strongly influenced by halide binding. To examine the role of the tryptophans (W139, W192, W238, and W249) in halide binding and catalysis, they were individually mutated to a phenylalanine. All mutations, except for W238F, influenced the enzymatic properties. Mutating W192 to phenylalanine inactivated the enzyme and led to dissociation into dimers and monomers. In the structure of HheC, residue W139 and residue W249 from the opposite subunit are close to the active site of the enzyme. Substitution of W139 mainly affected K(m) values with all tested substrates and reduced the enantiopreference for p-nitro-2-bromo-1-phenylethanol. Replacing W249 increased both k(cat) and K(m) values with all tested substrates except for the (S)-enantiomer of p-nitro-2-bromo-1-phenylethanol, for which k(cat) was 3-fold decreased, resulting in a 6-fold increase of the enantioselectivity. Fluorescence measurements revealed that in the ligand-free state the intrinsic protein fluorescence of mutant W139F is higher than that of the wild-type enzyme, while the fluorescence intensity of mutants W238F and W249F was lower. The fluorescence intensities of the W238F and W249F enzymes were increased when they were unfolded or when bromide was added, whereas the fluorescence of mutant W139F was not increased by unfolding or addition of bromide. These results demonstrate that the fluorescence of residues W238 and W249 is partially quenched in the folded ligand-free state, and that W139 is completely quenched and acts as an energy acceptor for the other tryptophan residues as well. Changes of the maximum fluorescence emission wavelength of the HheC variants and the results of acrylamide quenching experiments confirmed that bromide binding induces a local conformational change around the active site, resulting in residue W139 and the quencher group being separated.

Structural, kinetic, and calorimetric characterization of the cold-active phosphoglycerate kinase from the antarctic Pseudomonas sp. TACII18

The gene encoding the phosphoglycerate kinase (PGK) from the Antarctic Pseudomonas sp. TACII18 has been cloned and found to be inserted between the genes encoding for glyceraldhyde-3-phosphate dehydrogenase and fructose aldolase. The His-tagged and the native recombinant PGK from the psychrophilic Pseudomonas were expressed in Escherichia coli. The wild-type and the native recombinant enzymes displayed identical properties, such as a decreased thermostability and a 2-fold higher catalytic efficiency at 25 degrees C when compared with the mesophilic PGK from yeast. These properties, which reflect typical features of cold-adapted enzymes, were strongly altered in the His-tagged recombinant PGK. The structural model of the psychrophilic PGK indicated that a key determinant of its low stability is the reduced number of salt bridges, surface charges, and aromatic interactions when compared with mesophilic and thermophilic PGK. Differential scanning calorimetry of the psychrophilic PGK revealed unusual variations in its conformational stability for the free and substrate-bound forms. In the free form, a heat-labile and a thermostable domain unfold independently. It is proposed that the heat-labile domain acts as a destabilizing domain, providing the required flexibility around the active site for catalysis at low temperatures.

Site-directed mutagenesis of proline 204 in the 'hinge' region of yeast phosphoglycerate kinase

Site-specific mutants have been produced in order to investigate the role of proline 204 in the 'hinge' region of yeast phosphoglycerate kinase (PGK). This totally conserved proline has been shown to be the only cis-proline in the high resolution crystal structures of yeast, B. stearothermophilus, T. brucei and T. maritima PGK, and may therefore have a role in the independent folding of the two domains or in the 'hinge' bending of the molecule during catalysis. The residue was replaced by a histidine (Pro204His) and a phenylalanine (Pro204Phe), and the resulting proteins characterised by differential scanning calorimetry (DSC), circular dichroism (CD), tryptophan fluorescence emission and kinetic analysis. Although the secondary and tertiary structure of the Pro204His protein is generally similar to that of the wild-type enzyme as assessed by CD, the enzyme is less stable to heat and guanidinium chloride denaturation than the wild-type. In the denaturation experiments two transitions were observed for both the wild-type and the Pro204His mutant, as have been previously reported for yeast PGK [Missiakas, D., Betton, J.M., Minard, P. & Yon, J.M. (1990) Biochemistry 29, 8683-8689]. The first transition is accompanied by an increase in fluorescence intensity leading to a hyperfluorescent state, followed by the second, corresponding to a decrease in fluorescence intensity. However, for the Pro204His mutant, the first transition proceeded at lower concentrations of guanidinium chloride and the second transition proceeded to the same extent as for the wild-type protein, suggesting that sequence-distant interactions are more rapidly disrupted in this mutant enzyme than in the wild-type enzyme, while sequence-local interactions are disrupted in a similar way. The Michaelis constants (K(m)) for both 3-phospho-D-glycerate and ATP are increased only by three or fourfold, which confirms that, as expected, the substrate binding sites are largely unaffected by the mutation. However, the turnover and efficiency of the Pro204His mutant is severely impaired, indicating that the mechanism of 'hinge' bending is hindered. The Pro204Phe enzyme was shown to be significantly less well folded than the wild-type and Pro204His enzymes, with considerable loss of both secondary and tertiary structure. It is proposed that the proline residue at 204 in the 'hinge' region of PGK plays a role in the stability and catalytic mechanism of the enzyme.

Effects of C-terminal deletions on the conformational state and denaturation of phosphoglycerate kinase

Phosphoglycerate kinase (PGK) contains two domains of approximately equal size, both of the alpha/beta type. An alpha-helix consisting of the middle section of the 415-amino acid polypeptide chain, and the N- and C-termini reside in the interdomain hinge region [Watson, H. C., et al. (1982) EMBO J. 1, 1635-1640]. The C-terminal end is an integral part of the N-terminal domain. The consequences of the deletion of fifteen and three C-terminal amino acids on the conformational state and on the guanidine hydrochloride-induced and thermal unfolding of PGK were investigated by using near- and far-UV CD, tryptophan fluorescence, 1-anilinonaphthalene-8-sulfonic acid binding, accessibility to chemical modification, and differential scanning calorimetry. The results of these studies indicate that the conformations of both domains and of the interdomain region were altered by these deletions. In the absence of the 15-amino acid C-terminal peptide [delta(401-415)], the N-terminal domain exhibits several characteristics of a molten globule state, whereas the C-terminal domain retains native-like, although distinctly different, tertiary structure. Deletion of three C-terminal amino acids [delta(413-415)] also globally affects PGK conformation, although to a much lesser extent. Both C-terminal deletions resulted in a significant decrease in protein stability, as demonstrated by their increased susceptibility to guanidine-induced and thermal denaturation. These results suggest that the formation of a native tertiary fold of PGK requires the presence of a complete polypeptide chain.

Kinetic studies of the refolding of yeast phosphoglycerate kinase: comparison with the isolated engineered domains

Unfolding and refolding kinetics of yeast phosphoglycerate kinase were studied by following the time-dependent changes of two signals: the ellipticity at 218 nm and 222 nm, and the fluorescence emission at 330 nm (following excitation at 295 nm). The protein is composed of two similar-sized structural domains. Each domain has been produced by recombinant DNA techniques. It has been previously demonstrated that the engineered isolated domains are able to fold into a quasinative structure (Minard, P., et al., 1989b, Protein Eng. 3, 55-60; Missiakas, D., Betton, J.M., Minard, P., & Yon, J.M., 1990, Biochemistry 29, 8683-8689). The behavior of the isolated domains was studied using the same two conformational probes as for the whole enzyme. We found that the refolding kinetics of each domain are multiphasic. In the whole protein, domain folding and pairing appeared to be simultaneous events. However, it was found that some refolding steps occurring during the refolding of the isolated C-domain are masked during the refolding of yeast phosphoglycerate kinase. The N-domain was also found to refold faster when it was isolated than when integrated.

Unfolding-refolding of the domains in yeast phosphoglycerate kinase: comparison with the isolated engineered domains

The role of domains as folding units was investigated with a two-domain protein, yeast phosphoglycerate kinase. Each of the domains was produced independently by site-directed mutagenesis. It has been previously demonstrated by several criteria that these domains are able to fold in vivo into a quasi-native structure [Minard et al. (1989a) Protein Eng. 3, 55-60; Fairbrother et al. (1989) Protein Eng. 3, 5-11]. In the present study, the reversibility of the unfolding-refolding process induced by guanidine hydrochloride was investigated for the intact protein and the isolated domains. The transitions were followed by circular dichroism for both domains and the intact protein and by the variations in enzyme activity for the intact protein. Tryptophan residues were used as intrinsic conformational probes of the C-domain. An extrinsic fluorescent probe, N-[[(iodoacetyl)amino]ethyl]-8-naphthylamine-1-sulfonic acid (IAEDANS), was bound to the unique cysteinyl residue Cys97 to observe the conformational events in the N-domain. The unfolding-refolding transitions of each domain in the intact protein and in the isolated domains prepared by site-directed mutagenesis were compared. It was shown that the two domains are able to refold in a fully reversible process. A hyperfluorescent intermediate was detected during the folding of both the isolated C-domain and the intact yeast phosphoglycerate kinase. The stability of each isolated domain was found to be similar, the free energy of unfolding being approximately half that of the intact molecule.

Assignment of the heterogeneous static and time-resolved tryptophan fluorescence of 3-phosphoglycerate kinase

The heterogeneous fluorescence of yeast 3-phosphoglycerate kinase, a hinge-bending enzyme with two tryptophan residues, has been resolved into three emission components using steady-state and time-resolved studies of the fluorescence quenching by acrylamide, iodide and caesium ions at different emission wavelengths. The buried Trp-333 has a blue-shifted heterogeneous emission spectrum characterised by three fluorescence lifetimes, and is inaccessible to quenchers. The surface Trp-308 also has a heterogeneous emission with multiple lifetimes. The emission of Trp-308 can be separated into a blue-shifted emission accessible to acrylamide and caesium only, and a red-shifted emission accessible to all three quenchers.

Frequency domain fluorescence studies of yeast phosphoglycerate kinase and its ternary complex

A frequency domain fluorescence study of yeast phosphoglycerate kinase has been performed to observe the effect of substrates on the structure and dynamics of the enzyme. At 20 degrees C and pH 7.2, a biexponential decay is observed for tryptophanyl emission. The short fluorescence lifetime (0.4 ns) component is associated with a spectrum having a 329-nm maximum and a 18.4-kJ/mol activation energy, Ea, for thermal quenching. The long-lifetime (3.5 ns) component has a 338-nm maximum and an Ea of only 7.9 kJ/mol. Tentatively we assign the short and long-lifetime components to Trp-333 and Trp-308. Binding of the substrates ATP and 3-phosphoglycerate leads to a significant increase in the fluorescence lifetime, the red shift of the emission spectrum and in the decrease in the Ea for both components. Acrylamide-quenching studies indicate that the two tryptophan residues have about the same degree of kinetic exposure to the quencher and that the binding of the substrates causes a very slight change in the quenching pattern. These fluorescence studies indicate that the binding of the substrates to phosphoglycerate kinase may influence the conformational dynamics around the two tryptophan residues located on one of the protein's domains.

Structural studies on yeast 3-phosphoglycerate kinase. Isolation by affinity chromatography and characterization of the peptides produced by cyanogen bromide cleavage. Location of the single cysteinyl residue in the primary structure

Cyanogen bromide cleavage of yeast 3-phosphoglycerate kinase yielded four fragments which account for the amino acid composition of the entire molecule. These results are consistent with a single polypeptide chain of molecular weight 42 000. Affinity chromatography on Sepharose-mercurial followed by gel filtration on Sephadex was used with success for separation of peptides. The carboxyl and N-terminal fragments were characterized. The N-terminal fragment contained the single cysteinyl residue of the protein. After cyanylation and subsequent cleavage, this cysteinyl residue was located near position 100.