{'fraction_non_alphanumeric': 0.027550260610573342, 'fraction_numerical': 0.014147431124348473, 'mean_word_length': 4.868995633187773, '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}}
Expanding the repertoire of an ERK2 recruitment site: cysteine footprinting identifies the D-recruitment site as a mediator of Ets-1 binding.

Many substrates of ERK2 contain a D-site, a sequence recognized by ERK2 that is used to promote catalysis. Despite lacking a canonical D-site, the substrate Ets-1 is displaced from ERK2 by peptides containing one. This suggests that Ets-1 may contain a novel or cryptic D-site. To investigate this possibility a protein footprinting strategy was developed to elucidate ERK2-ligand interactions. Using this approach, single cysteine reporters were placed in the D-recruitment site (DRS) of ERK2 and the resulting ERK2 proteins subjected to alkylation by iodoacetamide. The ability of residues 1-138 of Ets-1 to protect the cysteines from alkylation was determined. The pattern of protection observed is consistent with Ets-1 occupying a hydrophobic binding site within the DRS of ERK2. Significantly, a peptide derived from the D-site of Elk-1, which is known to bind the DRS, exhibits a similar pattern of cysteine protection. This analysis expands the repertoire of the DRS on ERK2 and suggests that other targeting sequences remain to be identified. Furthermore, cysteine-footprinting is presented as a useful way to interrogate protein-ligand interactions at the resolution of a single amino acid.