Functional Determinants of Temperature Adaptation in Enzymes of Cold- versus Warm-Adapted Mussels (Genus Mytilus)

Abstract

Temperature is a strong selective force on the evolution of proteins due to its effects on higher orders of protein structure and, thereby, on critical protein functions like ligand binding and catalysis. Comparisons among orthologous proteins from differently thermally adapted species show consistent patterns of adaptive variation in function, but few studies have examined functional adaptation among multiple structural families of proteins. Thus, with our present state of knowledge, it is difficult to predict what fraction of the proteome will exhibit adaptive variation in the face of temperature increases of a few to several degrees Celsius, that is, temperature increases of the magnitude predicted by models of global warming. Here, we compared orthologous enzymes of the warm-adapted Mediterranean mussel Mytilus galloprovincialis and the cold-adapted Mytilus trossulus, a native of the North Pacific Ocean, species whose physiologies exhibit significantly different responses to temperature. We measured the effects of temperature on the kinetics (Michaelis-Menten constant-K(m)) of five enzymes that are important for ATP generation and that represent distinct protein structural families. Among phosphoglucomutase (PGM), phosphoglucose isomerase (PGI), pyruvate kinase (PK), phosphoenolpyruvate carboxykinase (GTP) (PEPCK), and isocitrate dehydrogenase (NADP) (IDH), only IDH orthologs showed significantly different thermal responses of K(m) between the two species. The K(m) of isocitrate of M. galloprovincialis-IDH was intrinsically lower and more thermally stable than that of M. trossulus-IDH and thus had higher substrate affinity at high temperatures. Two amino acid substitutions account for the functional differences between IDH orthologs, one of which allows for more hydrogen bonds to form near the mobile region of the active site in M. galloprovincialis-IDH. Taken together, our findings cast light on the targets of adaptive evolution in the context of climate change; only a minority of proteins might adapt to small changes in temperature, and these adaptations may involve only small changes in sequence.

Heat-resistant cytosolic malate dehydrogenases (cMDHs) of thermophilic intertidal snails (genus Echinolittorina): protein underpinnings of tolerance to body temperatures reaching 55°C

“…These observations can be interpreted in part by the results of the MD simulations, which showed that ErcMDH had a significantly greater overall flexibility, as indexed by the RMSD value, at higher temperature than EmcMDH. The difference in temperature adaptation between EmcMDH and ErcMDH orthologs is consistent with that seen in dehydrogenase enzymes in other molluscan species that occur at different heights in the intertidal zone and/or at different latitudes (Dong and Somero, 2009;Lockwood and Somero, 2012;Fields et al, 2015).…”

“…These are sites where evolutionary trade-off between activity and stability may be especially important (Tattersall et al, 2012;Zeiske et al, 2016). A potential general pattern in temperature adaptation of enzymes was proposed that conjectured that the sensitivity of an enzyme to temperature and, thereby, the intensity of selection for temperature adaptation of structure depends on the degree of conformational change that the enzyme undergoes during catalysis (Lockwood and Somero, 2012). Thus, selection would be expected to favor conservation of local flexibility in these regions of the protein across species (corresponding states of structure) and, for a given species, across its normal range of cellular temperatures.…”

Adaptations of protein structure and function to temperature: there is more than one way to ‘skin a cat’

“…Whereas we currently cannot determine what proportion of proteins in the proteome must adapt to increases in temperature of a few degrees Celsius, there are some data suggesting that not all proteins may be as sensitive to temperature as LDH-A and cMDH. For example, in comparisons of orthologous variants of six enzymes in ATP-generating pathways of the congeneric blue mussels M. galloprovincialis and M. trossulus, only two enzymes, cMDH (Fields et al, 2006) and isocitrate dehydrogenase (IDH) (Lockwood and Somero, 2012), showed adaptive variation. No differences in temperature versus K m responses were seen for phosphoglucomutase, phosphoglucose isomerase, phosphoenolpyruvate carboxykinase or pyruvate kinase (Lockwood and Somero, 2012).…”

“…Proteins from bacteria and Archaea, for example, often have served to elucidate broad patterns in protein adaptation across wide temperature ranges, and have allowed researchers to define general criteria for structural adaptation to temperature (D'Amico et al, 2003;Siddiqui and Cavicchioli, 2006;Feller, 2008Feller, , 2010Gu and Hilser, 2009). In contrast, studies of enzyme orthologs from closely related species of ectothermic metazoans, such as phosphoglucose isomerase in butterflies (Watt et al, 2003), pyruvate kinase in fish (Low and Somero, 1976) and isocitrate dehydrogenase in mussels (Lockwood and Somero, 2012), have the potential to reveal the minimum amount of environmental temperature change necessary to induce modifications in enzyme function and structure, and what types and magnitudes of amino acid substitutions are sufficient to allow adaptation to a new thermal environment. Of these latter types of studies focusing on orthologs from closely related species, among the most fruitful have been a series of studies using A 4 -lactate dehydrogenase (A 4 -LDH) and cytosolic malate dehydrogenase (cMDH).…”

Behavior and survival ofMytiluscongeners following episodes of elevated body temperature in air and seawater

“…Mytilus galloprovincialis evolved in the warmer Mediterranean Sea and invaded southern California waters sometime in the twentieth century, while the other two species are native to the region (reviewed by Lockwood and Somero, 2011). The physiological consequences of these divergent evolutionary histories include different thermal performance characteristics of certain metabolic enzymes (Fields et al, 2006;Lockwood and Somero, 2012), differences in the thermal limits of cardiac function (Braby and Somero, 2006b), and disparate transcriptomic and proteomic responses to a single episode of elevated body temperature in SW between the blue mussels (Lockwood et al, 2010;Tomanek and Zuzow, 2010). These biochemical, physiological and molecular differences all are consistent with interspecific differences in susceptibility to thermal stress.…”