Abstract:
The present study provides a deeper view of protein
functionality as a function of temperature, salt and
pressure in deep-sea habitats. A set of eight different
enzymes from five distinct deep-sea (3040–4908 m
depth), moderately warm (14.0–16.5°C) biotopes,
characterized by a wide range of salinities (39–348
practical salinity units), were investigated for this
purpose. An enzyme from a ‘superficial’ marine
hydrothermal habitat (65°C) was isolated and characterized
for comparative purposes. We report here the
first experimental evidence suggesting that in saltsaturated
deep-sea habitats, the adaptation to high
pressure is linked to high thermal resistance (P
value = 0.0036). Salinity might therefore increase the
temperature window for enzyme activity, and possibly
microbial growth, in deep-sea habitats. As an
example, Lake Medee, the largest hypersaline deepsea
anoxic lake of the Eastern Mediterranean Sea,
where the water temperature is never higher than
16°C, was shown to contain halopiezophilic-like
enzymes that are most active at 70°C and with denaturing
temperatures of 71.4°C. The determination of
the crystal structures of five proteins revealed
unknown molecular mechanisms involved in protein
adaptation to poly-extremes as well as distinct active
site architectures and substrate preferences relative
to other structurally characterized enzymes.
