peptacular 1.3.0

A spectacularly simple package for working with peptide sequences.

Peptacular

A spectacularly simple package for working with peptide sequences.

ReadTheDocs

https://peptacular.readthedocs.io/en/latest/index.html

Installation

pip install peptacular

Modification Notation:

• Term modifications (N-terminus and C-terminus) are specified using square brackets: [].
• Residue modifications within the sequence are specified using parentheses: ().

Modification Types:

• Modifications can be represented as strings, integers, or floats.
• During parsing, the module automatically identifies the modification type based on its representation.

Working with Sequences

from peptacular import sequence

# Create modified peptide sequence, mods can be str, float or int, 'PEPTIDE' -> 'P(1.2345)EPTID(1)E[Amide]'
peptide = sequence.add_modifications('PEPTIDE', {0: 1.2345, 5: 1, 7: 'Amide'})
assert peptide == 'P(1.2345)EPTID(1)E[Amide]'

# Parse modifications from peptide sequence, 'P(1.2345)EPTID(1)E[Amide]' -> {0:1.2345, 5:1, 7:'Amide'}
parsed_modifications = sequence.get_modifications(peptide)
assert parsed_modifications == {0: 1.2345, 5: 1, 7: 'Amide'}

# Strip modifications from peptide sequence, 'P(1.2345)EPTID(1)E[Amide]' -> 'PEPTIDE'
stripped_peptide = sequence.strip_modifications(peptide)
assert stripped_peptide == 'PEPTIDE'

Calculating mass and m/z

from peptacular.mass import calculate_mass, calculate_mz

# Calculate mass (monoisotopic)
peptide_mass = calculate_mass('PEP(1.0)TIDE[2.0]', charge=2)
assert peptide_mass == 804.3745169602499

# Calculate m/z (monoisotopic)
peptide_mz = calculate_mz('PEP(1.0)TIDE[2.0]', charge=2)
assert peptide_mz == 402.18725848012497

# Calculate m/z (average)
peptide_mz = calculate_mz('PEP(1.0)TIDE[2.0]', charge=2, monoisotopic=False)
assert peptide_mz == 402.42130880862

Building Fragment Ions

from peptacular.fragment import fragment

# Calculate the m/z values for the y+ fragments. Order [y5+, y4+, ..., y1+]
fragments = fragment('P(1.0)TIDE[2.0]', ion_types='y', charges=1, monoisotopic=True)
assert fragments == [577.27188355666, 479.21911970781, 378.17144123940005,
                     265.08737726227, 150.06043423844]

# Or for multiple ion types and charges. Order: [y3+, y2+, y1+, y3++, y2++, y1++, b3+, ...,  b1++]
fragments = fragment('P(1.0)EP', ion_types=['y', 'b'], charges=[1, 2], monoisotopic=True)
assert fragments == [343.16596193614004, 245.11319808729002, 116.07060499932,
                     172.08661920145502, 123.06023727703, 58.538940733045,
                     325.15539725244, 228.10263340359, 99.06004031562,
                     163.08133685960502, 114.55495493517999, 50.033658391195004]


# Using average mass
fragment('PEPTIDE', ion_types=['y', 'b'], charges=[1, 2], monoisotopic=False)

# Calculate fragment masses instead of m/z values
fragment('PEPTIDE', ion_types=['y', 'b'], charges=[1, 2], monoisotopic=True, mz=False)

Digesting Sequences

from peptacular.digest import digest

# Can use enzyme name from Constants.PROTEASES
peptides = digest('TIDERTIDEKT(1)IDE[2]', enzyme_regex='trypsin/P', missed_cleavages=2)
assert set(peptides) == {'TIDER', 'TIDERTIDEK', 'TIDERTIDEKT(1)IDE[2]', 'TIDEK',
                    'TIDEKT(1)IDE[2]', 'T(1)IDE[2]'}

# or use a custom regex
peptides = digest('TIDERTIDEKT(1)IDE[2]', enzyme_regex='([KR])', missed_cleavages=2)
assert set(peptides) == {'TIDER', 'TIDERTIDEK', 'TIDERTIDEKT(1)IDE[2]', 'TIDEK',
                    'TIDEKT(1)IDE[2]', 'T(1)IDE[2]'}

# Also supports semi-enzymatic digestion (might want to use min/max len to filter)
peptides = digest('TIDERTIDEKT(1)IDE[2]', enzyme_regex='trypsin/P', missed_cleavages=2,
                  semi=True, min_len=10)
assert set(peptides) == {'TIDERTIDEK', 'TIDERTIDEKT(1)IDE[2]', 'TIDERTIDEKT(1)ID', 'TIDERTIDEKT(1)I',
                    'TIDERTIDEKT(1)', 'IDERTIDEKT(1)IDE[2]', 'DERTIDEKT(1)IDE[2]',
                    'ERTIDEKT(1)IDE[2]', 'RTIDEKT(1)IDE[2]'}

Static and Variable Modifications

from peptacular.sequence import apply_static_modifications, apply_variable_modifications

# Apply static modifications
peptide = apply_static_modifications('PEPTIDE[2]', {'P': 'phospho', '(?<=P)E': 1})
assert peptide == 'P(phospho)E(1)P(phospho)TIDE[2]'

# Apply variable modifications
peptides = apply_variable_modifications('PEPTIDE[2]', {'P': 'phospho', '(?<=P)E': 1}, max_mods=2)
assert peptides == ['P(phospho)E(1)PTIDE[2]', 'P(phospho)EP(phospho)TIDE[2]', 'P(phospho)EPTIDE[2]',
                    'PE(1)P(phospho)TIDE[2]', 'PE(1)PTIDE[2]', 'PEP(phospho)TIDE[2]', 'PEPTIDE[2]']