You are studying the effects of amino acid replacements on the stability of a pa

Question

You are studying the effects of amino acid replacements on the stability of a particular alpha-helix that is buried in the protein myoglobin. You carry out a site-specific mutagenesis. The replacements you make are as follows: Leu->Arg, Leu-> Val, Leu->Pro, Leu->Gly, Leu_>Ala

a.For each replacement, predict whether the change would stabilize, destabalize, or have no effect on the structure of the alpha-helix. Briefly explain each of you predictions.

b. For each replacement, write the most likely mRNA codon required to code for that particular amino acid substitution. Which of the replacement can be carried out by single-base changes? Which of the replacements can be produced only by altering two bases in the mRNA codon?

C.

Substitution Effect Prediction Prediction explanation Codon # of changes Leu->Arg Leu->Val Leu->Pro Leu->Gly Leu->Ala

Explanation / Answer

Substitution effect prediction prediction explanation codon # of changes Leu->Arg No effect The helical propensity of Leu and Arg are same that is 0.21 Kcal/mol CUC->>CGC Single base change Leu->Val Stabilize The helical propensity of Leu is 0.21 Kcal/mol and that of Val is 0.61 Kcal/mol CUC->>GUC Single base change Leu->Pro Destabilize The helical propensity of Leu is 0.21 Kcal/mol and that of Pro is 3.16 Kcal/mol CUC->>CCC Single base change Leu->Gly Destabilize The helical propensity of Leu is 0.21 Kcal/mol and that of Gly is 1.00 Kcal/mol CUC->>GGC Two base changes Leu->Ala Stabilize The helical propensity of Leu is 0.21 Kcal/mol and that of Ala is 0 Kcal/mol CUC->>GCC Two base changes

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