The deep biosphere experiences extreme hydrostatic pressures and temperature variation, yet enzymes remain functional under these conditions. How protein sequences encode catalytic efficiency and stability in such environments remains poorly understood, particularly with respect to pressure. To address this, we examined extracellular nucleases (exNucs) homologous to Staphylococcus aureus nuclease (SNase) from deep-sea organisms to elucidate molecular signatures of pressure adaptation. Phylogenetic analyses relative to SNase indicate that nucleases from deep-sea organisms are distantly related. We recently showed that a nuclease from Carnobacterium sp., isolated at ∼2,500 m and ∼2 °C from the Aleutian Trench, is a bona fide exonuclease despite a highly negative electrostatic surface. Structural modeling, SAXS, and NMR indicate that CNase largely conserves the SNase fold and folding mechanism despite low sequence identity. The enzyme is mostly unfolded at basic pH (pH > 7.5) but, upon addition of Ca 2+ , becomes both folded and active. High-pressure NMR/SAXS/fluorescence and pressure-jump kinetics show a late folding transition state, with most cavity formation and solvent exclusion occurring at the kinetic barrier—behavior conserved with SNase. High-pressure stopped-flow activity measurements show pressure-independent kinetics for SNase up to ∼1 kbar, whereas CNase activity becomes pressure-sensitive above ∼400 bar. Ongoing comparative studies with deep-sea exNucs from D. piezophilus (1,639 m; Mediterranean Sea sediments) and G. kaustoiphilus (10,985 m; Challenger Deep, Mariana Trench), which exhibit intermediate surface electrostatics relative to CNase and SNase, will test whether tuning of electrostatics and local packing modulates excited-state equilibria and pressure responses across this enzyme family. Together, these results begin to map sequence-encoded strategies by which enzymes preserve folding and function in the high-pressure ocean.
Koduru et al. (2026) studied this question.