Reverse turns in textbooks always connect antiparallel beta-strands. Well what a

Question

Reverse turns in textbooks always connect antiparallel beta-strands. Well what about connecting antiparallel alpha-helices?

a. Make a flowchart that presents the logical basis of a computer program to identify reverse turns connecting antiparallel alpha-helices. Such connections would have residue i as the ending and residue i+3 as the starting residue of the connected pair of helices.

b. What is an example of a reverse turn connecting alpha-helices in a real protein structure?

c. Model a sterically allowed reverse turn between antiparallel alpha-helices.

d. Can you predict limitations on the type of residue that occupies position i+1 or i+2 of the turn?

Explanation / Answer

a . The computer program should search for hydrogen bond--------> If hydrogen bond is between COO- of 1st amino acid (i)-------> and NH3+ of 3rd amino acid (i+3)-------> mark as reverse turn-----> if i+3 is first and i is last-----> mark as reverse turn connecting antiparallel alpha helices.

b. Globular proteins generally have this kind of turn.

c. and d. The i+2 residue should always be glycine.This is the main point of consideration. Then only antiparallel alpha helix is allowed.

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