Before computing {D, U}-valued sequence of length five around each amino acid, let me explain the notation used.
One letter representation of ... is defined as follows.
(Step 1) ...
For example, the sequence of all D corresponds to binary number 00000 and its value is 0. DDDDU corresponds to binary number 00001 and its value is 1. And so on.
(Step 2) ...
For example, DUDDU corresponds to binary number 01001, whose value is 9. Thus numeral "9" is assigned. On the other hand, DUDUD corresponds to binary number 01010, whose value is 10. Then, alphabet "A" is assigned.