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momvart/BLOSUM62.py

Created April 8, 2020 17:48
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Simple BLOSUM62 implementation in python. Used for sequence alignment of proteins. Based on https://en.wikipedia.org/wiki/BLOSUM
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BLOSUM62.py
BLOSUM62_MATRIX = [[4, 0, -2, -1, -2, 0, -2, -1, -1, -1, -1, -2, -1, -1, -1, 1, 0, 0, -3, -2],
[0, 9, -3, -4, -2, -3, -3, -1, -3, -1, -1, -3, -3, -3, -3, -1, -1, -1, -2, -2],
[-2, -3, 6, 2, -3, -1, -1, -3, -1, -4, -3, 1, -1, 0, -2, 0, -1, -3, -4, -3],
[-1, -4, 2, 5, -3, -2, 0, -3, 1, -3, -2, 0, -1, 2, 0, 0, -1, -2, -3, -2],
[-2, -2, -3, -3, 6, -3, -1, 0, -3, 0, 0, -3, -4, -3, -3, -2, -2, -1, 1, 3],
[0, -3, -1, -2, -3, 6, -2, -4, -2, -4, -3, 0, -2, -2, -2, 0, -2, -3, -2, -3],
[-2, -3, -1, 0, -1, -2, 8, -3, -1, -3, -2, 1, -2, 0, 0, -1, -2, -3, -2, 2],
[-1, -1, -3, -3, 0, -4, -3, 4, -3, 2, 1, -3, -3, -3, -3, -2, -1, 3, -3, -1],
[-1, -3, -1, 1, -3, -2, -1, -3, 5, -2, -1, 0, -1, 1, 2, 0, -1, -2, -3, -2],
[-1, -1, -4, -3, 0, -4, -3, 2, -2, 4, 2, -3, -3, -2, -2, -2, -1, 1, -2, -1],
[-1, -1, -3, -2, 0, -3, -2, 1, -1, 2, 5, -2, -2, 0, -1, -1, -1, 1, -1, -1],
[-2, -3, 1, 0, -3, 0, 1, -3, 0, -3, -2, 6, -2, 0, 0, 1, 0, -3, -4, -2],
[-1, -3, -1, -1, -4, -2, -2, -3, -1, -3, -2, -2, 7, -1, -2, -1, -1, -2, -4, -3],
[-1, -3, 0, 2, -3, -2, 0, -3, 1, -2, 0, 0, -1, 5, 1, 0, -1, -2, -2, -1],
[-1, -3, -2, 0, -3, -2, 0, -3, 2, -2, -1, 0, -2, 1, 5, -1, -1, -3, -3, -2],
[1, -1, 0, 0, -2, 0, -1, -2, 0, -2, -1, 1, -1, 0, -1, 4, 1, -2, -3, -2],
[0, -1, -1, -1, -2, -2, -2, -1, -1, -1, -1, 0, -1, -1, -1, 1, 5, 0, -2, -2],
[0, -1, -3, -2, -1, -3, -3, 3, -2, 1, 1, -3, -2, -2, -3, -2, 0, 4, -3, -1],
[-3, -2, -4, -3, 1, -2, -2, -3, -3, -2, -1, -4, -4, -2, -3, -3, -2, -3, 11, 2],
[-2, -2, -3, -2, 3, -3, 2, -1, -2, -1, -1, -2, -3, -1, -2, -2, -2, -1, 2, 7]]
CHAR_INDEX = [0, -1, 1, 2, 3, 4, 5, 6, 7, -1, 8, 9, 10,
11, -1, 12, 13, 14, 15, 16, -1, 17, 18, -1, 19, -1]
def blosum62(first, second):
first = first.upper()
second = second.upper()
f_index = ord(first) - ord('A')
s_index = ord(second) - ord('A')
return BLOSUM62_MATRIX[CHAR_INDEX[f_index]][CHAR_INDEX[s_index]]
assert blosum62('A', 'Y') == -2
assert blosum62('M', 'P') == -2
assert blosum62('W', 'W') == 11
assert blosum62('R', 'N') == 0
assert blosum62('I', 'V') == 3
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