biostudies-literatureTinklepaugh JIchor TherapeuticsResearch Corporation for Scientific AdvancementCenter for Advanced Systems and Engineering, Syracuse UniversityCentre National de la Recherche ScientifiqueInstitut National de la Santé et de la Recherche MédicaleNational Institute of General Medical SciencesNIGMS NIH HHS7141-7145https://www.ebi.ac.uk/biostudies/studies/S-EPMC5664142biostudies-literatureUnknown2(10)Saposin B (SapB) is a human lysosomal protein, critical for the degradation of <i>O</i>-sulfogalactosylceramide (sulfatide). SapB binds sulfatide and presents it to the active site of the enzyme arylsulfatase A. Deficiency of SapB leads to fatal activator-deficient metachromatic leukodystrophy. Given the conformational flexibility and the large hydrophobic "pocket" produced upon (physiologically relevant) homodimerization, SapB may have broader substrate diversity than originally thought. Herein, we present evidence using fluorescence spectroscopy and computational docking studies that SapB binds a wide variety of ligands at <i>K</i>_D values varying from micromolar to nanomolar, with entropy being the primary driving force. We further demonstrate, for the first time, that SapB has two binding sites that can sequentially (and in a preferred order) accommodate up to two ligands at once.ACS omegaExploring the Multiligand Binding Specificity of Saposin B Reveals Two Binding Sites.PMC56641427892R15 GM104879R15GM104879Smith BMBou-Abdallah FHanlon EDoyle RPTinklepaugh JZubieta CfalseExploring the Multiligand Binding Specificity of Saposin B Reveals Two Binding Sites.Saposin B (SapB) is a human lysosomal protein, critical for the degradation of <i>O</i>-sulfogalactosylceramide (sulfatide). SapB binds sulfatide and presents it to the active site of the enzyme arylsulfatase A. Deficiency of SapB leads to fatal activator-deficient metachromatic leukodystrophy. Given the conformational flexibility and the large hydrophobic "pocket" produced upon (physiologically relevant) homodimerization, SapB may have broader substrate diversity than originally thought. Herein, we present evidence using fluorescence spectroscopy and computational docking studies that SapB binds a wide variety of ligands at <i>K</i>_D values varying from micromolar to nanomolar, with entropy being the primary driving force. We further demonstrate, for the first time, that SapB has two binding sites that can sequentially (and in a preferred order) accommodate up to two ligands at once.2017-01-01T00:00:00Z2017 Oct2024-11-09T23:23:06.945Z2019-03-27T03:00:31ZS-EPMC56641422910495310.1021/acsomega.7b01334