biopython v1.71.0 Bio.Alphabet.IUPAC.ExtendedIUPACProtein

Extended uppercase IUPAC protein single letter alphabet including X etc.

In addition to the standard 20 single letter protein codes, this includes:

  • B = “Asx”; Aspartic acid (R) or Asparagine (N)
  • X = “Xxx”; Unknown or ‘other’ amino acid
  • Z = “Glx”; Glutamic acid (E) or Glutamine (Q)
  • J = “Xle”; Leucine (L) or Isoleucine (I), used in mass-spec (NMR)
  • U = “Sec”; Selenocysteine
  • O = “Pyl”; Pyrrolysine

This alphabet is not intended to be used with X for Selenocysteine (an ad-hoc standard prior to the IUPAC adoption of U instead).