Related Experiment Videos
Compactness of protein molten globules: temperature-induced structural changes of the apomyoglobin folding
K Gast1, H Damaschun, R Misselwitz
1Max-Delbrück-Center for Molecular Medicine Berlin-Buch, Germany.
Abstract:
Apomyoglobin undergoes a two-step unfolding transition when the pH is lowered from 6 to 2. The partly folded intermediate (I) state at pH 4 and low ionic strength has properties of a molten globule. We have studied structural features of this state, its compactness, content of secondary structure, and specific packing of aromatic side chains, using dynamic light scattering, and small-angle X-ray scattering and far- and near-ultraviolet circular dichroism spectroscopy. Particular attention was paid to temperature-dependent structural changes. The results are discussed with reference to the native-like (N) state and the highly unfolded (U) state. It turned out that the I-state is most compact near 30 degrees C, having a Stokes radius 20% larger and a radius of gyration 30% larger than those of the N-state. Both cooling and heating relative to 30 degrees C led to an expansion of the molecule, but the structural changes at low and high temperatures were of a different kind. At temperatures above 40 degrees C non co-operative melting of structural elements was observed, while the secondary structure was essentially retained on cooling. The results are discussed in context with theoretical predictions of the compactness and the stability of apomyoglobin by Alonso et al. [Alonso, D. O. V., Dill, K. A., and Stigter, D. (1991) Biopolymers 31:1631-1649]. Comparing the I-state of apomyoglobin with the molten globules of alpha-lactalbumin and cytochrome c, we found that the compactness of the molten globule states of the three proteins decreases in the order alpha-lactalbumin > apocytochrome c > apomyoglobin.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Apomyoglobin
Area of Science:
- Protein structure and folding
- Biophysical chemistry
Background:
- Apomyoglobin exhibits a two-step unfolding transition as pH decreases.
- A partially folded intermediate (I) state at pH 4 resembles a molten globule.
Purpose of the Study:
- To investigate the structural characteristics of apomyoglobin's molten globule intermediate state.
- To analyze temperature-dependent structural changes and compare them to native and unfolded states.
Main Methods:
- Dynamic light scattering
- Small-angle X-ray scattering
- Far- and near-ultraviolet circular dichroism spectroscopy
Main Results:
- The intermediate state is most compact around 30°C, with increased Stokes radius and radius of gyration compared to the native state.
- Structural changes upon cooling and heating differ; non-cooperative melting occurs above 40°C, while secondary structure is retained on cooling.
- The molten globule state of apomyoglobin is less compact than those of alpha-lactalbumin and cytochrome c.
Conclusions:
- Apomyoglobin's intermediate state displays molten globule characteristics with distinct temperature-dependent structural dynamics.
- These findings provide insights into protein folding pathways and the nature of molten globule states.