Question

23. Consider these three sequences contained within single beta strands. Which is most likely to have ionic interactions between side chains at physiological pH? Explain your choice. Sequence 1: Ala-Glu- Leu- Arg Sequence 2: Ala - Glu - Arg-Leu Sequence 3: Leu - Ala - Glu- Arg 24. The equilibrium between the native state (N) and the unfolded state (U) of a protein can be represented by the chemical equation N U, with a AG value that represents the equilibrium. A. Which one of the following proteins is the least stable in its folded conformation? Protein A: AG+1.25 Protein B. AG" -+1.50 Protein C: AG-0.33 Stability data for GBI variants B. So ΔGo is a measure of protein stability. Consider the chart at right (Lassila et al., Protoin Sci 2002) with ariant values for ΔG° and two related Tm C) AHTm (kcal/mol) 4G (75 C) (kcal/mol) RER44 79.1 05 53.5 2 0.61 variables measuring the stability of eight variants of the GB1 domain of a Rs3A44 76.1 0.4 523 20 protein called Protein G 0.16 R6A53R44 69.603 45.0 16 0.74 How do Tm, 4Hrm and AG(75°C) relateReAsA4 706+03 466+1s to protein stability? -0.62 0.79 6EszR44 80.10.6 56.1+2.5 6E53444 77.2+04 54.1+1.9 034 6AS3R44 75.5+0.3 so.1 15 0.08 eAS3A44 76.0 0.3 514 16 What doos it mean for the proteins that T-midpoint of thermal denaturation transition; have a nogative AG(75°C)? Doos this AH enthalpy of folding at T protein spontaneously unfold at biological conditions? Δα75°C): free energy of folding calculated at 750. C. The crystal structure of the GB1 of Protein G is shown at right (from the same reference). The domain has been used as an experimental system for examining the beta sheet forming propensity of amino acids. By definition, backbone hydrogen bonds are required to form this structure, but interactions between side chain atoms can further stabilize-or destabilize-a Glu53 beta sheet structure. What do the data from this paper tell us? Specifically, how can one explain decrease in Tm when comparing RsEsR (first row of the Table 1, above, stucture pictured at right) to REAsR4 (third row of Table 1)? Arg44

Answer 1

Answer 23:-

Sequence 2: Ala-Glu-Arg-Leu is most likely to have ionic interactions between side chains at physiological pH. This is because amongst charged amino acids, Glutamic Acid (Glu) is negatively charged and Arginine (Arg) is positively charged. The current sequence makes it the most likely one to provide ionic interactions.