worksheet 9

worksheet 9 - Worksheet 9 G = H TS G Free Energy =...

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Worksheet 9 1 ∆G = ∆H - T∆S ∆G – Free Energy = difference between unfolded and native state - Folding has to compensate this energy difference. - Smaller ∆G = easier to fold ∆H – Enthalpy = energy of non-covalent interactions w/in peptide chain - Ex. Hydrogen bonding, Hydrophobic interactions, Ionic Bonds - Covalent interactions (peptide bond) don’t change - In the native state, non-covalent interactions are maximized (stronger). ∆S – Entropy = energy required to maintain order as nature tends towards disorder. - Folded state is highly ordered. - This energy opposes enthalpy. T M = Melting Temperature - Temperature at which the protein begins to unfold. - Fig. 17.4 shows the increase in melting temperature as a result of artificially introducing disulfide bonds into a polypeptide chain. The bar represents the difference between the oxidized (S-S bond) and reduced (no S-S bond) states. Protein Stability – Engineering Proteins 1. Disultide Bridges - Higher # of unfolded conformations in a protein – higher entropic cost to fold into native state. - Increase (artificially) # of disulfide bonds = more stable. - Can be in loops or between motifs. 2. Gly and Pro - Gly allows more freedom, decreasing stability. - Pro adds constraints, increasing stability. - But don’t want to change the main chain interactions to the point of disrupting function. 3. Dipole Stability - N-terminal: + charged (- charged ions are usually bond to this) - C-terminal: - changed - Dipole Compensating Residues: in alpha helices not found in binding sites of proteins, there will be – charged residues as the terminating N-term residue and + charged residues as the terminating C-term residue (to compensate the charges of the main chain). 4.
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worksheet 9 - Worksheet 9 G = H TS G Free Energy =...

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