2. S100A6 is a signaling protein that interacts with another protein, SIP, to regulate protein degradation activity in cells. The S100A6/SIP interaction can be described as the following reaction: Kp S100A6 : SIP S100A6 + SIP The Kp is 2 µM. The structure of the S100A6/SIP interaction is shown below. S100A6 is shown as a blue surface, SIP as an orange peptide. A conserved methionine residue on SIP (spheres in center of figure) interacts with a hydrophobic pocket on S100A6. (a) Draw a curve showing the fraction saturation of S100A6 with increasing concentrations of SIP, labeling the Kp on the curve. (Feel free to make in Excel). (b) Would you predict mutating the Met to a Leu or Lys would be more disruptive to binding? Please justify your answer. (c) Draw the fractional saturation vs. [SIP] curve for your mutant curve, clearly labeling how it differs from the wildtype curve you drew in (a).

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Chapter1: Biochemistry: An Evolving Science
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### Understanding S100A6 and SIP Interaction

**Overview:**
S100A6 is a signaling protein that interacts with another protein, SIP, to regulate protein degradation activity in cells. The interaction between S100A6 and SIP can be described by the equilibrium reaction:

\[ S100A6 : SIP \rightleftharpoons S100A6 + SIP \]

The dissociation constant (\( K_D \)) for this interaction is 2 µM.

**Structure Representation:**
- **S100A6** is depicted with a blue surface.
- **SIP** is shown as an orange peptide.
- A conserved methionine residue on SIP is highlighted by spheres (shown in the center) interacting with a hydrophobic pocket on S100A6.

![Structural Diagram](Insert here the description of the image if uploaded online)

**Diagram Explanation:**
The image presents a structural model where:
- The blue surface represents the S100A6 protein.
- The orange helix represents the SIP peptide.
- The spheres indicating the methionine residue emphasize the interaction within a hydrophobic pocket on S100A6.

**Exercises:**

(a) **Fractional Saturation Curve:**
   - Draw a curve showing the fractional saturation of S100A6 with increasing concentrations of SIP. Label the dissociation constant (\( K_D \)) on the curve. (It can be created in Excel).

(b) **Mutation Prediction:**
   - Predict whether mutating the methionine (Met) to leucine (Leu) or lysine (Lys) would more disruptively affect binding. Provide justification for your prediction.

(c) **Mutant Curve Analysis:**
   - Draw the fractional saturation versus [SIP] curve for your mutant, and clearly label how it differs from the wild-type curve you created in part (a).

These exercises aim to deepen the understanding of protein interactions and the impact of mutations on binding affinity.
Transcribed Image Text:### Understanding S100A6 and SIP Interaction **Overview:** S100A6 is a signaling protein that interacts with another protein, SIP, to regulate protein degradation activity in cells. The interaction between S100A6 and SIP can be described by the equilibrium reaction: \[ S100A6 : SIP \rightleftharpoons S100A6 + SIP \] The dissociation constant (\( K_D \)) for this interaction is 2 µM. **Structure Representation:** - **S100A6** is depicted with a blue surface. - **SIP** is shown as an orange peptide. - A conserved methionine residue on SIP is highlighted by spheres (shown in the center) interacting with a hydrophobic pocket on S100A6. ![Structural Diagram](Insert here the description of the image if uploaded online) **Diagram Explanation:** The image presents a structural model where: - The blue surface represents the S100A6 protein. - The orange helix represents the SIP peptide. - The spheres indicating the methionine residue emphasize the interaction within a hydrophobic pocket on S100A6. **Exercises:** (a) **Fractional Saturation Curve:** - Draw a curve showing the fractional saturation of S100A6 with increasing concentrations of SIP. Label the dissociation constant (\( K_D \)) on the curve. (It can be created in Excel). (b) **Mutation Prediction:** - Predict whether mutating the methionine (Met) to leucine (Leu) or lysine (Lys) would more disruptively affect binding. Provide justification for your prediction. (c) **Mutant Curve Analysis:** - Draw the fractional saturation versus [SIP] curve for your mutant, and clearly label how it differs from the wild-type curve you created in part (a). These exercises aim to deepen the understanding of protein interactions and the impact of mutations on binding affinity.
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