Answer the following questions based upon an a-helix with the sequence SE1WYSSVH

Question

Answer the following questions based upon an a-helix with the sequence SE1WYSSVHLDKTAFQ and using the diagram below. A helical wheel diagram is a representation of an a-helix oriented as if you were looking up from the bottom of the helix. Complete the helical wheel diagram by writing in the 3 letter code for each amino acid in the appropriate circle. The number corresponds to the sequence order. Based upon your knowledge of the amino acid side chains, indicate on the diagram the half of the helix that would face the inside of a globular protein by putting a bracket around it The half should include 8 amino acids. Are there any amino acids that look out of place on the indicated side? If so, what are they and provide an example of how they might be accommodated on the inside of the protein. This alpha-helix is part of a signaling protein that is regulated by post-translation modifications (or PTMs). Thyroperoxidase is an enzyme that iodinates Tyrosine residues on proteins (substituting iodine for hydrogen on the aromatic ring, making monoiodotyrosine or diiodotyrosine). Thyroperoxidase can only art upon tyrosines exposed on the surface. Indicate where this PTM will occur on the diagram above. When this PTM occurs, the Pk_A of the tyrosine shifts, causing this side chain to become charged. As a result, this signaling peptide is able to form a stronger interaction with its binding partner, enhancing the signal transduction in the cell. Monoiodination gives a 2-fold enhancement in the binding interaction, but diiodination causes a 10-fold enhancement in the binding interaction. Explain chemically why this change in binding interaction would occur. Please make your answer fit in the given box.

Explanation / Answer

1.

SEIWYSSVHLDKTAFQ

Ser, Glu, Ile, Trp, Tyr, Ser, Ser, Val, His, Leu, Asp, Lys, Asp, Lys, Thr, Ala, Phe, Gln.

2. Hydrophobic amino acids are present inside the globular protein.

Ser, Glu, (Ile), (Trp), (Tyr), Ser, Ser, (Val), His, (Leu), Asp,Lys, Asp, Lys, Thr, (Ala), (Phe), Gln.

3. Histidine become neutral charge at Ph-7. So, His goes inside the globular protein.

4. Tyr 5th amino acid.

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