def removeModifications(peptide):
    """Removes all modifications from a peptide string and return the plain
    amino acid sequence.

    :param peptide: peptide sequence, modifications have to be written in the
        format "[modificationName]"
    :param peptide: str

    :returns: amino acid sequence of ``peptide`` without any modifications
    """
    while peptide.find('[') != -1:
        peptide = peptide.split('[', 1)[0] + peptide.split(']', 1)[1]
    return peptide