{'fraction_non_alphanumeric': 0.013888888888888888, 'fraction_numerical': 0.004629629629629629, 'mean_word_length': 5.091549295774648, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Structural basis of chaperone self-capping in P pilus biogenesis.

PapD is an immunoglobulin-like chaperone that mediates the assembly of P pili in uropathogenic strains of Escherichia coli. It binds and caps interactive surfaces on pilus subunits to prevent their premature associations in the periplasm. We elucidated the structural basis of a mechanism whereby PapD also interacts with itself, capping its own subunit binding surface. Crystal structures of dimeric forms of PapD revealed that this self-capping mechanism involves a rearrangement and ordering of the C2-D2 and F1-G1 loops upon dimerization which might ensure that a stable dimer is not formed in solution in spite of a relatively large dimer interface. An analysis of site directed mutations revealed that chaperone dimerization requires the same surface that is otherwise used to bind subunits.