def get_gene_onto(pdb_id):
    """Return ligands of given PDB_ID

    Parameters
    ----------

    pdb_id : string
        A 4 character string giving a pdb entry of interest

    Returns
    -------

    out : dict
        A dictionary containing the gene ontology information associated with the entry

    Examples
    --------

    >>> gene_info = get_gene_onto('4Z0L')
    >>> print(gene_info['term'][0])
    {'@chainId': 'A',
     '@id': 'GO:0001516',
     '@structureId': '4Z0L',
     'detail': {'@definition': 'The chemical reactions and pathways resulting '
                               'in the formation of prostaglandins, any of a '
                               'group of biologically active metabolites which '
                               'contain a cyclopentane ring.',
                '@name': 'prostaglandin biosynthetic process',
                '@ontology': 'B',
                '@synonyms': 'prostaglandin anabolism, prostaglandin '
                             'biosynthesis, prostaglandin formation, '
                             'prostaglandin synthesis'}}
    """
    out = get_info(pdb_id, url_root = 'http://www.rcsb.org/pdb/rest/goTerms?structureId=')
    out = to_dict(out)
    if not out['goTerms']:
        return None
    out = remove_at_sign(out['goTerms'])
    return out
Return ligands of given PDB_ID

    Parameters
    ----------

    pdb_id : string
        A 4 character string giving a pdb entry of interest

    Returns
    -------

    out : dict
        A dictionary containing the gene ontology information associated with the entry

    Examples
    --------

    >>> gene_info = get_gene_onto('4Z0L')
    >>> print(gene_info['term'][0])
    {'@chainId': 'A',
     '@id': 'GO:0001516',
     '@structureId': '4Z0L',
     'detail': {'@definition': 'The chemical reactions and pathways resulting '
                               'in the formation of prostaglandins, any of a '
                               'group of biologically active metabolites which '
                               'contain a cyclopentane ring.',
                '@name': 'prostaglandin biosynthetic process',
                '@ontology': 'B',
                '@synonyms': 'prostaglandin anabolism, prostaglandin '
                             'biosynthesis, prostaglandin formation, '
                             'prostaglandin synthesis'}}