{'fraction_non_alphanumeric': 0.039122137404580155, 'fraction_numerical': 0.01049618320610687, 'mean_word_length': 5.357575757575757, '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}}
A Single Approach Reveals the Composite Conformational Changes, Order of Binding, and Affinities for Calcium Binding to Calmodulin.

We found that a newly developed method named LITPOMS (ligand titration, fast photochemical oxidation of proteins and mass spectrometry) can characterize section-by-section of a protein the conformational changes induced by metal-ion binding. Peptide-level LITPOMS applied to Ca2+ binding to calmodulin reveals binding order and site-specific affinity, providing new insights on the behavior of proteins upon binding Ca2+. We established that EF hand-4 (EF-4) binds calcium first, followed by EF-3, EF-2, and EF-1 and determined the four affinity constants by modeling the extent-of-modification curves. We also found positive cooperativity between EF-4, EF-3 and EF-2, EF-1 and allostery involving the four EF-hands. LITPOMS recapitulates via one approach the calcium-calmodulin binding that required decades of sophisticated development to afford versatility, comprehensiveness, and outstanding spatial resolution.