title: The Lysosomal Protein Saposin B Binds Chloroquine.
abstract: Chloroquine (CQ) has been widely used in the treatment of malaria since the 1950s, though toxicity and resistance is increasingly limiting its use in the clinic. More recently, CQ is also becoming recognized as an important therapeutic compound for the treatment of autoimmune disorders and has shown activity as an anticancer agent. However, the full extent of CQ pharmacology in humans is still unclear. Herein, we demonstrate that the lysosomal protein saposin B (sapB), critical for select lipid degradation, binds CQ with implications for both CQ function and toxicity. Using isothermal titration calorimetry (ITC) and fluorescence quenching experiments, CQ was shown to bind to the dimeric form of sapB at both pH 5.5 and pH 7.4 with an average binding affinity of 2.3×10(4)  m(-1). X-ray crystallography confirmed this, and the first complete crystal structure of sapB with a bound small molecule (CQ) is reported. The results suggest that sapB might play a role in mitigating CQ-based toxicity and that sapB might itself be overwhelmed by CQ causing impaired lipid degradation.
authors.affiliation: Department of Chemistry, Syracuse University, 111 College Place, Syracuse, NY, 13244, USA.
authors.forename: Brian P
authors.initials: BP
authors.lastname: Huta
authors.affiliation: Department of Chemistry, State University of New York at Potsdam, Potsdam, NY, 13676, USA.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Mehlenbacher
authors.affiliation: Department of Chemistry, Syracuse University, 111 College Place, Syracuse, NY, 13244, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Nie
authors.affiliation: European Synchrotron Radiation Facility, Grenoble, 38054, France.
authors.forename: Xuelei
authors.initials: X
authors.lastname: Lai
authors.affiliation: Laboratoire de Physiologie Cellulaire & Végétale, iRTSV, UMR 5168, CNRS/CEA/INRA/Univ. Grenoble Alpes, Grenoble, 38054, France. chloe.zubieta@cea.fr.
authors.forename: Chloe
authors.initials: C
authors.lastname: Zubieta
authors.affiliation: Department of Chemistry, State University of New York at Potsdam, Potsdam, NY, 13676, USA. bouabdf@potsdam.edu.
authors.forename: Fadi
authors.initials: F
authors.lastname: Bou-Abdallah
authors.affiliation: Department of Chemistry, Syracuse University, 111 College Place, Syracuse, NY, 13244, USA. rpdoyle@syr.edu.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Doyle
mesh_terms: D001665:Binding Sites; D002151:Calorimetry; D002738:Chloroquine / Q000737:chemistry* / Q000378:metabolism* / Q000633:toxicity; D018360:Crystallography, X-Ray; D005453:Fluorescence; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D015394:Molecular Structure; D049231:Saposins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D049231:Saposins; D002738:Chloroquine
keywords: chloroquine; isothermal titration calorimetry; lysosomes; malaria; protein crystal structures; saposin B