The pressure-induced, reversible inactivation of mouse brain enolases

The Energetics of Streptococcal Enolase Octamer Formation: The Quantitative Contributions of the Last Eight Amino Acids at the Carboxy-Terminus

The enolase produced by Streptococcus pyogenes is a homo-octamer whose overall shape resembles that of a donut. The octamer is best described as a tetramer of dimers. As such, it contains two types of interfaces. The first is common to almost all enolases as most enolases that have been studied are dimers. The second is unique to the octamers and includes residues near the carboxy-terminus. The primary sequence of the enolase contains 435 residues with an added 19 as an N-terminal hexahistine tag. We have systematically truncated the carboxy-terminus, individually removing the first 8 residues. This gave rise to a series of eight structures containing respectively, 435, 434, 433, 432, 431, 430, 429 and 427 residues. The truncations cause the protein to gradually dissociate from octamers to enzymatically inactive monomers with very small amounts of intermediate tetramers and dimers. We have evaluated the contributions of the missing residues to the monomer/octamer equilibrium using a combination of analytical ultracentrifugation and activity assays. For the dissociation reaction, octamer ⇐⇒ 8 monomer truncation of all eight C-terminal residues resulted in a diminution in the standard Gibbs energy of dissociation of about 59 kJ/mole of octamer relative to the full length protein. Considering that this change is spread over eight subunits, this translates to a change in standard Gibbs interaction energy of less than 8 kJ/mole of monomer distributed over the eight monomers. The resulting proteins, containing 434, 433, 432, 431, 430, 429 and 427 residues per monomer, showed intermediate free energies of dissociation. Finally, three other mutations were introduced into our reference protein to establish how they influenced the equilibrium. The main importance of this work is it shows that for homo-multimeric proteins a small change in the standard Gibbs interaction energy between subunits can have major physiological effects.

Water as it applies to the function of enzymes

Escherichia coli and Saccharomyces cerevisiae can metabolize, grow, and divide over osmotic pressures ranging from 0.24 atm to about 100 atm [Record, T. M. et al. (1999). Trends Biochem. Sci. 23,143-148,190-194; Wood, J. M. (1999). Microbiol. Mol. Bio. Rev. 63, 230-262; Marachal, P. A., and Gervais, P. (1994). Appl. Microbiol. Biotechnol. 42, 617-622]. At the higher end of the range, they perform their functions with difficulty, but they can survive. Over the full span of pressures, the activity of water goes from 0.9998 to 0.93. Neither of the authors can survive at anything like these extremes; some of their enzymes and enzymatic complexes would "fall apart," would either cease to function or would denature. We would very much like to know just how the two microbes manage.

Cloning, expression and mutagenesis of a subunit contact of rabbit muscle-specific (betabeta) enolase

The cDNA for rabbit muscle-specific (betabeta) enolase was cloned, sequenced and expressed in Escherichia coli. This betabeta-enolase differs at eight positions from that sequenced by Chin (17). Site-directed mutagenesis was used to change residue 414 from glutamate to leucine, thereby abolishing a salt bridge involved in subunit contacts. Recombinant wild-type and mutant enolase were purified from E. coli and compared to enolase isolated from rabbit muscle. Molecular weights were determined by mass spectrometry. All three betabeta-enolases had similar kinetics, and UV and circular dichroism (CD) spectra. The mutant enolase was far more sensitive to inactivation by pressure, by KCl or EDTA, and by sodium perchlorate. We confirmed, by analytical ultracentrifugation, that the sodium perchlorate inactivation was due to dissociation. DeltaG(o) for dissociation of enolase was decreased from 49.7 kJ/mol for the wild-type enzyme to 42.3 kJ/mol for the mutant. In contrast to the wild-type enzyme, perchlorate inactivation of E414L was accompanied by a small loss of secondary structure.

The effects of osmotic and hydrostatic pressures on macromolecular systems

Osmotic pressure and hydrostatic pressure can be used effectively to probe the behavior of biologically important macromolecules and their complexes. Using the two techniques requires a theoretical framework as well as knowledge of the more common pitfalls. Both are discussed in this review in the context of several examples.

Structural and functional effects of hydrostatic pressure on centrosomes from vertebrate cells

In an attempt to better understand the role of centrioles in vertebrate centrosomes, hydrostatic pressure was applied to isolated centrosomes as a means to disassemble centriole microtubules. Treatments of the centrosomes were monitored by analyzing their protein composition, ultrastructure, their ability to nucleate microtubules from pure tubulin, and their capability to induce parthenogenetic development of Xenopus eggs. Moderate hydrostatic pressure (95 MPa) already affected the organization of centriole microtubules in isolated centrosomes, and also impaired microtubule nucleation. At higher pressure, the protein composition of the peri-centriolar matrix (PCM) was also altered and the capacity to nucleate microtubules severely impaired. Incubation of the treated centrosomes in Xenopus egg extract could restore their capacity to nucleate microtubules after treatment at 95 MPa, but not after higher pressure treatment. However, the centriole structure was in no case restored. It is noteworthy that centrosomes treated with mild pressure did not allow parthenogenetic development after injection into Xenopus eggs, even if they had recovered their capacity to nucleate microtubules. This suggested that, in agreement with previous results, centrosomes in which centriole architecture is impaired, could not direct the biogenesis of new centrioles in Xenopus eggs. Centriole structure could also be affected by applying mild hydrostatic pressure directly to living cells. Comparison of the effect of hydrostatic pressure on cells at the G1/S border or on the corresponding cytoplasts suggests that pro-centrioles are very sensitive to pressure. However, cells can regrow a centriole after pressure-induced disassembly. In that case, centrosomes eventually recover an apparently normal duplication cycle although with some delay.

The salt-induced dissociation and inactivation of a mammalian enolase: evidence for the formation of active monomers

The gamma gamma isozyme of rabbit enolase was labeled with fluorescein and the effects of NaClO4 on both enzymatic activity and fluorescence polarization were studied. NaClO4, but not NaCl, dissociates and partially inactivates the enzyme. If dissociation is prevented, either by the addition of substrate or by covalently crosslinking the enzyme, inactivation is also prevented. Analysis of the time and concentration dependence of inactivation and dissociation shows that the decrease in activity is a two-step process: D in equilibrium 2M in equilibrium 2M*. Both monomeric forms of the enzyme are catalytically active.

A reactor permitting injection and sampling for steady state studies of enzymatic reactions at high pressure: tests with aspartate transcarbamylase

A high pressure reactor for steady state studies of enzymes is described. It allows injection, stirring, and sampling without release of the pressure (up to at least 400 MPa). Thus, either substrate or enzyme can be injected to initiate an enzyme-catalyzed reaction whose progress can then be followed by measurements on samples taken from the reactor. The dead time of sampling is 10-15 s, which allows reactions with pseudo-first-order rate constants smaller than about 1 min-1 to be monitored. It can be used for any enzymatic reaction; unlike previously described high pressure apparatus, it is not limited to the study of enzymes whose activity can be directly followed by spectrophotometry. The use and reliability of this reactor is demonstrated by tests with aspartate transcarbamylase. The activity of this enzyme is enhanced by pressures of the order of 120 MPa.

Complex of brain D-phosphoglycerate mutase and gamma enolase and its reactivation by D-glycerate 2,3-bisphosphate

The dissociabilities of dimeric gamma enolase, alpha enolase, and phosphoglycerate mutase of brain origin were tested using fluorescein isothiocyanate attached covalently to these enzymes. The dissociation constant of dimeric gamma enolase is lower (Kd = 0.03 microM) than that of the alpha enolase (Kd = 3 microM), while dimeric mutase seems to be nondissociable in the concentration range 0.1-10 microM, at pH 7.3 in 50 mM imidazole buffer at 20 degrees C. Interaction of neuron-specific gamma enolase with D-phosphoglycerate mutase was detected with the same fluorescence-labeling technique as well as by a kinetic analysis. The determined dissociation constant of the enolase-mutase complex was found to be in the range 5-40 microM, independent of the technique used. A mixed type of inhibition in the binding of D-glycerate-2-P and mutase to the D-glycerate-2-P binding site on enolase was observed in the absence of D-glycerate-2,3-P2. However, the inhibition of the enolase activity by brain D-phosphoglycerate mutase in the D-glycerate-2-P----phosphoenolpyruvate transformation is almost fully reverted by D-glycerate-2,3-P2, probably via the proper coordination of the active centers in the ternary complex of enolase, D-phosphoglycerate mutase, and their common intermediate, D-glycerate-2-P. The mechanism of intermediate transfer by consecutive enzyme pairs in a nondivergent metabolite flux (around the transformation of D-glycerate-2-P) is examined and conclusions of the present experiments are compared with the results of an extended analysis performed earlier with a divergent metabolite flux (around the transformation of multiusage triosephosphates, D-glyceraldehyde-3-P, and dihydroxyacetone phosphate).

Inactivation of NAD-dependent dehydrogenases from shallow- and deep-living fishes by hydrostatic pressure and proteolysis

Cytoplasmic malate dehydrogenase [L)-malate:NAD+ oxidoreductase, EC 1.1.1.37) and glyceraldehyde-3-phosphate dehydrogenase (D-glyceraldehyde-3-phosphate:NAD+ oxidoreductase, EC 1.2.1.12) homologues from two shallow-living and three deep-living fishes were examined for the effects of hydrostatic pressure on enzyme activity and susceptibility to inactivation by proteinases. These studies were done to determine whether malate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase homologues show similar patterns of adaptation to hydrostatic pressure as seen in lactate dehydrogenase (L-lactate:NAD+ oxidoreductase, EC 1.1.1.27) homologues from the same species (Hennessey, J.P., Jr. and Siebenaller, J.F. (1987) J. Exp. Zool. 241, 9-15). Fish malate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase homologues are much less susceptible to inactivation by hydrostatic pressure than are lactate dehydrogenase homologues from the same species. This difference in susceptibility to inactivation by hydrostatic pressure may be due to the decreased number of intersubunit contacts in malate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase homologues relative to lactate dehydrogenase homologues. Inactivation of malate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase homologues by proteinases, both at atmospheric pressure and at elevated hydrostatic pressure, is less than for lactate dehydrogenase homologues from the same species. This suggests that the structural characteristics and conformational perturbations that are responsible for the susceptibility of lactate dehydrogenase to proteolytic inactivation are not found in malate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase homologues of the same species.

The pressure-induced inactivation of mammalian enolases is accompanied by dissociation of the dimeric enzyme

The effects of exposure to pressure on both the activity and the quaternary structure of rabbit brain enolases, forms alpha alpha, alpha gamma, and gamma gamma were studied in the pressure range of 1 to 3400 bar. Effects on quaternary structure were determined by subunit scrambling (the formation of alpha alpha and gamma gamma from alpha gamma or vice versa). All three dimers are stable up to pressures of 1200 bar. The dissociation of gamma gamma begins at 1200 bar, yielding a stable monomer; inactivation of gamma gamma does not begin until the pressure is greater than 2000 bar. Dissociation of gamma gamma is not accompanied by changes in the tryptophan fluorescence of the protein. However, the fluorescence does decrease when the pressure is greater than 2000 bar, the point at which inactivation of gamma gamma starts. The alpha monomer, on the other hand, is unstable in the pressure range that produces dissociation of alpha alpha. This process, which also begins at 1200 bar, is paralleled by inactivation. Crosslinking the enzyme with glutaraldehyde demonstrated that the inactive form of the enzyme is monomeric. The pressure-induced inactivation of these forms of enolase is thus clearly a two-step process, with both dissociation and inactivation occurring. The difference in pressure sensitivity of rabbit brain alpha alpha and gamma gamma is due to a difference in stability of the alpha and gamma monomers and not due to a difference in the pressures required for dissociation.