Folding intermediates of hyperthermophilic D‐glyceraldehyde‐3‐phosphate dehydrogenase from Thermotoga maritima are trapped at low temperature

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Abstract
D-Glyceraldehyde-3-phosphate dehydrogenase from the hyperthermophilic eubacterium, Thermotoga maritima, is extremely thermostable showing a thermal transition beyong 105°C. At low temperature, ‘cold denaturation’ becomes detectable only in the presence of destabilizing agents. Reconstitution after preceding denaturation depends on temperature. At 0°C, no significant recovery of activity is detectable, whereas between 30 and 100°C reactivation reaches up to 85%. Shifting the temperature from low values to the range of optimum reconstitution releases the trapped intermediate in a fast reaction. Evidence from ultra-centrifugal analysis and far-UV circular dichroism proves the intermediate to be partially assembled to the tetramer, with most of its native secondary structure restored in a fast reaction. Fluorescence emission exhibits at least biphasic kinetics with the rate-limiting step(s) reflecting local adjustments of aromatic residues involved in tertiary contacts in the native state of the enzyme.