Thermodynamic and Structural Adaptation Differences between the Mesophilic and Psychrophilic Lactate Dehydrogenases

Sergei Khrapunov, Eric Chang, Robert Callender

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

The thermodynamics of substrate binding and enzymatic activity of a glycolytic enzyme, lactate dehydrogenase (LDH), from both porcine heart, phLDH (Sus scrofa; a mesophile), and mackerel icefish, cgLDH (Chamapsocephalus gunnari; a psychrophile), were investigated. Using a novel and quite sensitive fluorescence assay that can distinguish protein conformational changes close to and distal from the substrate binding pocket, a reversible global protein structural transition preceding the high-temperature transition (denaturation) was surprisingly found to coincide with a marked change in enzymatic activity for both LDHs. A similar reversible structural transition of the active site structure was observed for phLDH but not for cgLDH. An observed lower substrate binding affinity for cgLDH compared to that for phLDH was accompanied by a larger contribution of entropy to Δ G, which reflects a higher functional plasticity of the psychrophilic cgLDH compared to that of the mesophilic phLDH. The natural osmolyte, trimethylamine N-oxide (TMAO), increases stability and shifts all structural transitions to higher temperatures for both orthologs while simultaneously reducing catalytic activity. The presence of TMAO causes cgLDH to adopt catalytic parameters like those of phLDH in the absence of the osmolyte. Our results are most naturally understood within a model of enzyme dynamics whereby different conformations of the enzyme that have varied catalytic parameters (i.e., binding and catalytic proclivity) and whose population profiles are temperature-dependent and influenced by osmolytes interconvert among themselves. Our results also show that adaptation can be achieved by means other than gene mutations and complements the synchronic evolution of the cellular milieu.

Original languageEnglish (US)
Pages (from-to)3587-3595
Number of pages9
JournalBiochemistry
Volume56
Issue number28
DOIs
StatePublished - Jul 18 2017

Fingerprint

Lactate Dehydrogenases
Thermodynamics
Substrates
Enzymes
Perciformes
Sus scrofa
Denaturation
Temperature
Transition Temperature
Entropy
L-Lactate Dehydrogenase
Plasticity
Conformations
Assays
Catalyst activity
Catalytic Domain
Proteins
Swine
Genes
Fluorescence

ASJC Scopus subject areas

  • Biochemistry

Cite this

Thermodynamic and Structural Adaptation Differences between the Mesophilic and Psychrophilic Lactate Dehydrogenases. / Khrapunov, Sergei; Chang, Eric; Callender, Robert.

In: Biochemistry, Vol. 56, No. 28, 18.07.2017, p. 3587-3595.

Research output: Contribution to journalArticle

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AB - The thermodynamics of substrate binding and enzymatic activity of a glycolytic enzyme, lactate dehydrogenase (LDH), from both porcine heart, phLDH (Sus scrofa; a mesophile), and mackerel icefish, cgLDH (Chamapsocephalus gunnari; a psychrophile), were investigated. Using a novel and quite sensitive fluorescence assay that can distinguish protein conformational changes close to and distal from the substrate binding pocket, a reversible global protein structural transition preceding the high-temperature transition (denaturation) was surprisingly found to coincide with a marked change in enzymatic activity for both LDHs. A similar reversible structural transition of the active site structure was observed for phLDH but not for cgLDH. An observed lower substrate binding affinity for cgLDH compared to that for phLDH was accompanied by a larger contribution of entropy to Δ G, which reflects a higher functional plasticity of the psychrophilic cgLDH compared to that of the mesophilic phLDH. The natural osmolyte, trimethylamine N-oxide (TMAO), increases stability and shifts all structural transitions to higher temperatures for both orthologs while simultaneously reducing catalytic activity. The presence of TMAO causes cgLDH to adopt catalytic parameters like those of phLDH in the absence of the osmolyte. Our results are most naturally understood within a model of enzyme dynamics whereby different conformations of the enzyme that have varied catalytic parameters (i.e., binding and catalytic proclivity) and whose population profiles are temperature-dependent and influenced by osmolytes interconvert among themselves. Our results also show that adaptation can be achieved by means other than gene mutations and complements the synchronic evolution of the cellular milieu.

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