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Protein Folding

Consider a small, natively disordered protein that exists in equilibrium with a highly ordered (folded) protein. At 37°C, the ratio of the disordered protein to ordered is 100 to 1. First, write an equilibrium expression (Keq) that describes this situation and calculate the corresponding Keq and free energy. Second, imagine that you combine the disordered protein and DNA and find that it both folds and binds the DNA with high affinity. The overall free energy of binding is calculated to be - 5.2 kcal/mol. Break down the binding to determine the actual free energy of binding of the folded protein with DNA. Finally, imagine that you're clever enough to engineer the protein to be more thermo-stable without affecting the DNA binding. In other words, the protein exists primarily in the folded form at equilibrium. What do you predict the Keq and ∆G for binding of the engineered protein to be when binding to DNA? Two hints: first draw a Schulz-energy diagram! This will guide you to the missing information you need. Second, if you didn't understand what I meant by engineering the protein, I'm suggesting that you could take the disordered protein in equilibrium with a small percentage of a folded protein and make amino acid changes such that it exists exclusively in the folded state. That's what I mean implied about it being more thermo-stable. This modified protein still binds the DNA target in the same way with the same affinity�"it just doesn't have to fold to achieve the correct binding conformation.

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Consider a small, natively disordered protein that exists in equilibrium with a highly ordered (folded) protein. At 37°C, the ...

Solution Summary

The equilibrium constant and free energy are calculated for protein folding.

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