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Favorable domain size in proteins
1Laboratory of Experimental and Computational Biology, IRSP, SAIC Frederick, NCI-FCRDC, MD 21702-1201, USA.
Folding & Design
|March 21, 1998
Summary
Protein domains favor a specific size range due to energetic balance. This balance, driven by interactions and entropy, dictates optimal protein folding and domain structure.
Area of Science:
- Biophysics
- Structural Biology
- Protein Folding
Background:
- Single-domain proteins and domains within multidomain proteins typically range from 100-150 amino acids.
- The origin of this favored protein size is not fully understood.
- Understanding protein size is crucial for predicting protein structure and function.
Purpose of the Study:
- To investigate the energetic factors that determine the optimal size of protein domains.
- To develop an empirical model for the free energy of unfolding as a function of chain length.
Main Methods:
- Constructed an empirical function for free energy of unfolding versus chain length.
- Derived function parameters by fitting to hydration energy, entropy, and enthalpy data from nine proteins.
- Validated the model against statistical analysis of experimentally determined protein domain structures.
Main Results:
- The model predicts an optimal domain size of 100 residues, corresponding to maximum free energy of unfolding.
- Short chains are unfavorable due to insufficient favorable enthalpy from inter-residue contacts.
- Long chains are unfavorable due to a quadratic increase in configurational entropy cost versus a linear increase in favorable enthalpy.
Conclusions:
- Energetic balance is the primary determinant of protein domain size.
- This energetic constraint forces large proteins to fold into multiple domains.
- The findings provide insights into the fundamental principles governing protein architecture.