title: Sulfatide Preserves Insulin Crystals Not by Being Integrated in the Lattice but by Stabilizing Their Surface.
abstract: BACKGROUND
  Sulfatide is known to chaperone insulin crystallization within the pancreatic beta cell, but it is not known if this results from sulfatide being integrated inside the crystal structure or by binding the surface of the crystal. With this study, we aimed to characterize the molecular mechanisms underlying the integral role for sulfatide in stabilizing insulin crystals prior to exocytosis.
  
  
  METHODS
  We cocrystallized human insulin in the presence of sulfatide and solved the structure by molecular replacement.
  
  
  RESULTS
  The crystal structure of insulin crystallized in the presence of sulfatide does not reveal ordered occupancy representing sulfatide in the crystal lattice, suggesting that sulfatide does not permeate the crystal lattice but exerts its stabilizing effect by alternative interactions such as on the external surface of insulin crystals.
  
  
  CONCLUSIONS
  Sulfatide is known to stabilize insulin crystals, and we demonstrate here that in beta cells sulfatide is likely coating insulin crystals. However, there is no evidence for sulfatide to be built into the crystal lattice.
authors.affiliation: Bartholin Instituttet, Rigshospitalet, 2100 Copenhagen, Denmark.
authors.forename: Karsten
authors.initials: K
authors.lastname: Buschard
authors.affiliation: Department of Pathology, Immunology and Laboratory Medicine, University of Florida College of Medicine, 1600 SW Archer Road, Gainesville, FL 32610, USA.
authors.forename: Austin W
authors.initials: AW
authors.lastname: Bracey
authors.affiliation: Department of Pathology, Immunology and Laboratory Medicine, University of Florida College of Medicine, 1600 SW Archer Road, Gainesville, FL 32610, USA.
authors.forename: Daniel L
authors.initials: DL
authors.lastname: McElroy
authors.affiliation: Department of Pathology, Immunology and Laboratory Medicine, University of Florida College of Medicine, 1600 SW Archer Road, Gainesville, FL 32610, USA.
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Magis
authors.affiliation: Bartholin Instituttet, Rigshospitalet, 2100 Copenhagen, Denmark.
authors.forename: Thomas
authors.initials: T
authors.lastname: Osterbye
authors.affiliation: Department of Pathology, Immunology and Laboratory Medicine, University of Florida College of Medicine, 1600 SW Archer Road, Gainesville, FL 32610, USA.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Atkinson
authors.affiliation: Department of Pathology, Immunology and Laboratory Medicine, University of Florida College of Medicine, 1600 SW Archer Road, Gainesville, FL 32610, USA.
authors.forename: Kate M
authors.initials: KM
authors.lastname: Bailey
authors.affiliation: Department of Pathology, Immunology and Laboratory Medicine, University of Florida College of Medicine, 1600 SW Archer Road, Gainesville, FL 32610, USA.
authors.forename: Amanda L
authors.initials: AL
authors.lastname: Posgai
authors.affiliation: Department of Pathology, Immunology and Laboratory Medicine, University of Florida College of Medicine, 1600 SW Archer Road, Gainesville, FL 32610, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Ostrov
mesh_terms: D000818:Animals; D003460:Crystallization; D006801:Humans; D007328:Insulin / Q000737:chemistry*; D050417:Insulin-Secreting Cells / Q000737:chemistry* / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D008958:Models, Molecular; D011487:Protein Conformation; D055550:Protein Stability; D011917:Rats, Inbred Lew; D013329:Structure-Activity Relationship; D013433:Sulfoglycosphingolipids / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D007328:Insulin; D013433:Sulfoglycosphingolipids