title: The structure of serine palmitoyltransferase; gateway to sphingolipid biosynthesis.
abstract: Sphingolipid biosynthesis commences with the condensation of L-serine and palmitoyl-CoA to produce 3-ketodihydrosphingosine (KDS). This reaction is catalysed by the PLP-dependent enzyme serine palmitoyltransferase (SPT; EC 2.3.1.50), which is a membrane-bound heterodimer (SPT1/SPT2) in eukaryotes such as humans and yeast and a cytoplasmic homodimer in the Gram-negative bacterium Sphingomonas paucimobilis. Unusually, the outer membrane of S. paucimobilis contains glycosphingolipid (GSL) instead of lipopolysaccharide (LPS), and SPT catalyses the first step of the GSL biosynthetic pathway in this organism. We report here the crystal structure of the holo-form of S. paucimobilis SPT at 1.3 A resolution. The enzyme is a symmetrical homodimer with two active sites and a monomeric tertiary structure consisting of three domains. The PLP cofactor is bound covalently to a lysine residue (Lys265) as an internal aldimine/Schiff base and the active site is composed of residues from both subunits, located at the bottom of a deep cleft. Models of the human SPT1/SPT2 heterodimer were generated from the bacterial structure by bioinformatics analysis. Mutations in the human SPT1-encoding subunit have been shown to cause a neuropathological disease known as hereditary sensory and autonomic neuropathy type I (HSAN1). Our models provide an understanding of how these mutations may affect the activity of the enzyme.
authors.affiliation: School of Chemistry, EaStCHEM, The University of Edinburgh, West Mains Road, Edinburgh, EH9 3JJ, Scotland, UK.
authors.forename: Beverley A
authors.initials: BA
authors.lastname: Yard
authors.forename: Lester G
authors.initials: LG
authors.lastname: Carter
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Johnson
authors.forename: Ian M
authors.initials: IM
authors.lastname: Overton
authors.forename: Mark
authors.initials: M
authors.lastname: Dorward
authors.forename: Huanting
authors.initials: H
authors.lastname: Liu
authors.forename: Stephen A
authors.initials: SA
authors.lastname: McMahon
authors.forename: Muse
authors.initials: M
authors.lastname: Oke
authors.forename: Daphné
authors.initials: D
authors.lastname: Puech
authors.forename: Geoffrey J
authors.initials: GJ
authors.lastname: Barton
authors.forename: James H
authors.initials: JH
authors.lastname: Naismith
authors.forename: Dominic J
authors.initials: DJ
authors.lastname: Campopiano
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000502:physiology; D001665:Binding Sites; D019295:Computational Biology; D019281:Dimerization; D020035:Holoenzymes / Q000737:chemistry; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D051102:Serine C-Palmitoyltransferase / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D013107:Sphingolipids / Q000096:biosynthesis*; D020578:Sphingomonas / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D020035:Holoenzymes; D021122:Protein Subunits; D013107:Sphingolipids; D051102:Serine C-Palmitoyltransferase