Survival Strategies in Cold-Adapted Microorganisms

Rubredoxin Protein Scaffolds Sourced from Diverse Environmental Niches as an Artificial Hydrogenase Platform

“…In native psychrophilic organisms, a more flexible backbone has been attributed to higher catalytic activity. 52 We note that Pg NiRd is more active for solution-phase hydrogen production than the previously studied Dd NiRd sequence. This same activity may not be seen on an electrode surface, as mobility may be specifically or nonspecifically constrained upon adsorption or attachment to an electrode, giving rise to the low electrochemical TOFs observed.…”

“…A large, negative Δ S ‡ is also seen in native enzymes from psychrophiles and is attributed to a large increase in order between the relatively relaxed ground state, with a high number of accessible microstates, and an organized transition state . The broader distribution of conformational states in the ground state is attributed to catalytic site flexibility. , A smaller, less negative Δ S ‡ is likewise seen for the Rds from the hyperthermophiles, Mj and Pf . Though NiRd has not naturally evolved to produce hydrogen gas, we consider it to be interesting that similar correlations between the parent organism growth temperature and Δ H ‡ and Δ S ‡ are observed across both engineered and naturally occurring enzymes.…”

“…Much work has been conducted to study sequence-based structural and dynamical differences that influence kinetic parameters and thermodynamic stability in naturally occurring enzymes. A variety of factors may contribute to the decreased thermostability of proteins from psychrophilic organisms, including fewer stabilizing residues such as isoleucine, which contribute to the hydrophobic effect, and lysine and glutamate residues, which have been suggested to increase thermostability through salt bridges and hydrogen-bonding interactions. − While variations differ across each protein, the decrease in thermostability is tightly linked to the need for psychrophiles to maintain enzymatic rates sufficient for the cellular function at low temperatures, which generally results in a more flexible protein framework . Work by Herschlag and coworkers mapped temperature-associated residues in hundreds of bacterial enzyme families and identified residues associated with both high and low growth temperatures .…”

“…A large, negative ΔS ‡ is also seen in native enzymes from psychrophiles and is attributed to a large increase in order between the relatively relaxed ground state, with a high number of accessible microstates, and an organized transition state. 52 The broader distribution of conformational states in the ground state is attributed to catalytic site flexibility. 52,53 A smaller, less negative ΔS ‡ is likewise seen for the Rds from the hyperthermophiles, Mj and Pf.…”

“…55−57 While variations differ across each protein, the decrease in thermostability is tightly linked to the need for psychrophiles to maintain enzymatic rates sufficient for the cellular function at low temperatures, which generally results in a more flexible protein framework. 52 Work by Herschlag and coworkers mapped temperature-associated residues in hundreds of bacterial enzyme families and identified residues associated with both high and low growth temperatures. 55 However, the sequences of the Rd variants selected in this work do not follow the residue trends seen across the large sample of bacterial enzyme families (Figure S33), highlighting that amino acid sequence is not (yet) sufficient to predict activity in this artificial enzyme.…”