Catalysis and Protein Folding in Psychrophiles
from: Cold-Adapted Microorganisms (Edited by: Isao Yumoto). Caister Academic Press, U.K. (2013)
Enzymes have the property to catalyze most of the chemical reactions occuring in living organisms and their efficiency is exponentially depending on temperature through the Arrhenius law. On the other hand psychrophiles are organisms that live in permanently cold habitats so, in the absence of adaptation, the rate of the chemical reactions would be to slow to sustain life. In fact, these organisms display, at the low temperature of their environment, metabolic fluxes close to that of their mesophilic counterparts. That means that their enzymes have been modified in order to compensate for the cooling effect on reaction rates. The analysis of the structure, catalytic properties and thermal stability of an already large number of psychrophilic enzymes has demonstrated that discrete changes in the amino acid sequence of these enzymes can confer a high catalytic efficiency at low and moderate temperatures. This is accompanied by a significant decrease of the thermal stability itself inducing a large increase of the flexibility of the molecular structure that enables the accomodation of the substrate even at temperatures lower than the freezing point of water. The folding process,which, in theory, is also rendered uneasy due to the large increase in viscosity, the low residual energy in the system and the depressive effect of low temperatures, notably on hydrophobic interactions, is also rescued, mainly, through the overexpression of peptidyl prolyl cis/trans isomerases and of the trigger factor which is the first to take in charge the nascent polypeptide chain read more ...