Bañares Hidalgo, ÁngelesPérez-Gil, JesúsEstrada, Pilar2023-06-182023-06-182016-07-05ESSN: 1932-620310.1371/journal.pone.0158430https://hdl.handle.net/20.500.14352/23387Assembly of pulmonary surfactant lipid-protein complexes depends on conformational changes coupled with proteolytic maturation of proSP-B, the precursor of pulmonary surfactant protein B (SP-B), along the surfactant biogenesis pathway in pneumocytes. Conformational destabilization of the N-terminal propeptide of proSP-B (SP-BN) triggers exposure of the mature SP-B domain for insertion into surfactant lipids. We have studied the conformational stability during GdmCl- or urea-promoted unfolding of SP-BN with trp fluorescence and circular dichroism spectroscopies. Binding of the intermediate states to bis-ANS suggests their molten globule-like character. ΔG0 H2O was ~ 12.7 kJ mol-1 either with urea or GdmCl. None of the thermal transitions of SP-BN detected by CD correspond to protein unfolding. Differential scanning calorimetry of SP-BN evidenced two endothermic peaks involved in oligomer dissociation as confirmed with 2 M urea. Ionic strength was relevant since at 150 mM NaCl, the process originating the endotherm at the highest temperature was irreversible (Tm2 = 108.5°C) with an activation energy of 703.8 kJ mol-1. At 500 mM NaCl the process became reversible (Tm2 = 114.4°C) and data were fitted to the Non-two States model with two subpeaks. No free thiols in the propeptide could be titrated by DTNB with or without 5.7 M GdmCl, indicating disulfide bonds establishment.engAtribución 3.0 Españajournal articlehttp://journals.plos.org/plosone/article?id=10.1371/journal.pone.0158430open access577.112UreaOligomersFluorescenceSedimentationSurfactantsProtein structureThermodynamicsDisulfide bondsBioquímica (Biología)2302 Bioquímica