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- Bjelic, Sinisa, et al.
(author)
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Cold adaptation of enzyme reaction rates
- 2008
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In: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 47:38, s. 10049-10057
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Journal article (peer-reviewed)abstract
- A major issue for organisms living at extreme temperatures is to preserve both stability and activity of their enzymes. Cold-adapted enzymes generally have a reduced thermal stability, to counteract freezing, and show a lower enthalpy and a more negative entropy of activation compared to mesophilic and thermophilic homologues. Such a balance of thermodynamic activation parameters can make the reaction rate decrease more linearly, rather than exponentially, as the temperature is lowered, but the structural basis for rate optimization toward low working temperatures remains unclear. In order to computationally address this problem, it is clear that reaction simulations rather than standard molecular dynamics calculations are needed. We have thus carried out extensive computer simulations of the keto-enol(ate) isomerization steps in differently adapted citrate synthases to explore the structure-function relationships behind catalytic rate adaptation to different temperatures. The calculations reproduce the absolute rates of the psychrophilic and mesophilic enzymes at 300 K, as well as the lower enthalpy and more negative entropy of activation of the cold-adapted enzyme, where the latter simulation result is obtained from high-precision Arrhenius plots. The overall catalytic effect originates from electrostatic stabilization of the transition state and enolate and the reduction of reorganization free energy. The simulations, however, show psychrophilic, mesophilic, and hyperthermophilic citrate synthases to have increasingly stronger electrostatic stabilization of the transition state, while the energetic penalty in terms of internal protein interactions follows the reverse order with the cold-adapted enzyme having the most favorable energy term. The lower activation enthalpy and more negative activation entropy observed for cold-adapted enzymes are found to be associated with a decreased protein stiffness. The origin of this effect is, however, not localized to the active site but to other regions of the protein structure.
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- van der Ent, Florian, et al.
(author)
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Structure and Mechanism of a Cold-Adapted Bacterial Lipase
- 2022
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In: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 61:10, s. 933-942
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Journal article (peer-reviewed)abstract
- The structural origin of enzyme cold-adaptation has been the subject of considerable research efforts in recent years. Comparative studies of orthologous mesophilic-psychrophilic enzyme pairs found in nature are an obvious strategy for solving this problem, but they often suffer from relatively low sequence identity of the enzyme pairs. Small bacterial lipases adapted to distinctly different temperatures appear to provide an excellent model system for these types of studies, as they may show a very high degree of sequence conservation. Here, we report the first crystal structures of lipase A from the psychrophilic bacterium Bacillus pumilus, which confirm the high structural similarity to the mesophilic Bacillus subtilis enzyme, as indicated by their 81% sequence identity. We further employ extensive QM/MM calculations to delineate the catalytic reaction path and its energetics. The computational prediction of a rate-limiting deacylation step of the enzymatic ester hydrolysis reaction is verified by stopped-flow experiments, and steady-state kinetics confirms the psychrophilic nature of the B. pumilus enzyme. These results provide a useful benchmark for examining the structural basis of cold-adaptation and should now make it possible to disentangle the effects of the 34 mutations between the two enzymes on catalytic properties and thermal stability.
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- Zavialov, Anton V, et al.
(author)
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Resolving the energy paradox of chaperone/usher-mediated fibre assembly
- 2005
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In: Biochemical Journal. - 0264-6021 .- 1470-8728. ; 389:Pt 3, s. 685-694
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Journal article (peer-reviewed)abstract
- Periplasmic chaperone/usher machineries are used for assembly of filamentous adhesion organelles of Gram-negative pathogens in a process that has been suggested to be driven by folding energy. Structures of mutant chaperone–subunit complexes revealed a final folding transition (condensation of the subunit hydrophobic core) on the release of organelle subunit from the chaperone–subunit pre-assembly complex and incorporation into the final fibre structure. However, in view of the large interface between chaperone and subunit in the pre-assembly complex and the reported stability of this complex, it is difficult to understand how final folding could release sufficient energy to drive assembly. In the present paper, we show the X-ray structure for a native chaperone–fibre complex that, together with thermodynamic data, shows that the final folding step is indeed an essential component of the assembly process. We show that completion of the hydrophobic core and incorporation into the fibre results in an exceptionally stable module, whereas the chaperone–subunit pre-assembly complex is greatly destabilized by the high-energy conformation of the bound subunit. This difference in stabilities creates a free energy potential that drives fibre formation.
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- Åqvist, Johan, et al.
(author)
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Molecular dynamics simulations of water and biomolecules wit a Monte Carlo constant pressure algorithm
- 2004
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In: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 384:4-6, s. 288-294
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Journal article (peer-reviewed)abstract
- A mixed molecular dynamics/Monte Carlo (MD/MC) algorithm for constant pressure simulations of arbitrary molecular systems is examined. Calculations are reported at ambient and high pressures both for liquid water systems and for a chemical reaction step in a solvated enzyme utilizing empirical valence bond potentials. The present method reproduces earlier reported results well and is computationally efficient since it does not require the virial to be evaluated at each MD step. It is also found that the effects of introducing MC volume steps on the dynamics of the system are negligible provided that the volume step sizes and updating frequencies are appropriately chosen.
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