Conformational transitions of cinnamoyl CoA reductase 1 from Leucaena leucocephala

• Earliest report on the conformational transition studies of L1-CCRH1 from Leucaena leucocephala.
• Characterization of acid induced molten globule.
• Rapid structural rearrangement and thermal aggregation at and above 50 °C.
• Different response of the molten globule towards thermal and chemical denaturation as compared to native protein.

Conformational transitions of cinnamoyl CoA reductase, a key regulatory enzyme in lignin biosynthesis, from Leucaena leucocephala (Ll-CCRH1) were studied using fluorescence and circular dichroism spectroscopy. The native protein possesses four trp residues exposed on the surface and 66% of helical structure, undergoes rapid structural transitions at and above 45 °C and starts forming aggregates at 55 °C. Ll-CCRH1 was transformed into acid induced (pH 2.0) molten globule like structure, exhibiting altered secondary structure, diminished tertiary structure and exposed hydrophobic residues. The molten globule like structure was examined for the thermal and chemical stability. The altered secondary structure of L1-CCRH1 at pH 2.0 was stable up to 90 °C. Also, in presence of 0.25 M guanidine hydrochloride (GdnHCl), it got transformed into different structure which was stable in the vicinity of 2 M GdnHCl (as compared to drastic loss of native structure in 2 M GdnHCl) as seen in far UV-CD spectra. The structural transition of Ll-CCRH1 at pH 2.0 followed another transition after readjusting the pH to 8.0, forming a structure with hardly any similarity to that of native protein.