The low-temperature folding intermediate of hyperthermophilic D-glyceraldehyde-3-phosphate dehydrogenase from Thermotoga maritima shows a native-like cooperative unfolding transition.

Hyperthermophilic D-glyceraldehyde-3-phosphate dehydrogenase from Thermotoga maritima, after denaturation in 6 M guanidinium chloride and subsequent renaturation by dilution at 3 degrees C, forms a 'low-temperature intermediate' with its native quaternary structure and most of its dichroic absorption restored, but with significant differences in its fluorescence properties compared to those of the native enzyme. Shifting the temperature beyond 10 degrees C, the enzyme is reconstituted to high yields and to an overall structure indistinguishable from the initial native state [FEBS Lett. 290 (1991) 235-238]. These criteria suggest that the cold intermediate represents an 'assembled molten globule'. However, present equilibrium transition data prove the cold intermediate to be native-like, in that it exhibits a reversible highly cooperative conformational transition to the unfolded state which is incompatible with the typical characteristics of the molten globule state of globular proteins.