In the same way, ...
The alpha-helix on the left is approximated by a folded tetrahedron sequence as shown in the middle. Then, the 2nd derivative of the tetrahedron sequence gives the binary sequence on the right.
Note that the four letters at both ends are all D.
That is, what the sequence describe ...
And it seems reasonable to compute short ...,
where maybe length five is enough, considering the above example.