Explorations into pressure-dependent flexibility mechanisms of ambient and deep-sea extremophilic bacterial enzymes

Discoveries of piezophiles - organisms that thrive under extreme pressure - raise questions towards the mechanisms behind the relationship between stability, flexibility, and activity of proteins, one of their central macromolecules. Approximately 88% of the ocean exists at high hydrostatic pressures (HHP), with these environments also comprising the largest portion of the biosphere. Studying biophysical processes engaged by these organisms can have implications on the origins of life, such as through theories in which primordial life began within deep-sea hydrothermal vents, and how life may possibly function deep within oceans of habitable exoplanets. Investigating the effects of HHP on the biophysical properties of proteins, in conjunction with structural adaptations utilized by known piezophilic organisms to maintain proper function, provide better insight into how organisms are affected by and survive at such depths. With recent advances into deep-sea exploration, genomic sequencing and high-pressure techniques, more knowledge can be gained towards understanding life at HHP.

Extended timescale graphics processing unit (GPU)-accelerated OpenMM molecular dynamics simulations were utilized to explore mechanisms behind pressure-effects on and pressure-adaptations within a central metabolic enzyme, dihydrofolate reductase (DHFR). In-silico comparisons were made between bacterial DHFRs of the mesophile (ambient pressure) Escherichia coli, the deep-sea piezophiles Moritella profunda and Moritella yayanosii, as well as mutants containing specific residues identified to be important in pressure-sensitivity. In addition, high-pressure small-angle neutron scattering, fluorescence and other high-pressure experimental techniques conducted up to 2 kbar further probed the biophysical effects of HHP on E. coli and M. profunda DHFRs. The combined results from in-silico and in-situ techniques provide enhanced insight into the interplay between the sequence, structure, and hydration of proteins underpinning life inhabiting extreme pressures.