Crystal structure of the human supernatant protein factor

Structure. 2002 Nov;10(11):1533-40. doi: 10.1016/s0969-2126(02)00884-5.


Supernatant protein factor (SPF) promotes the epoxidation of squalene catalyzed by microsomes. Several studies suggest its in vivo role in the cholesterol biosynthetic pathway by a yet unknown mechanism. SPF belongs to a family of lipid binding proteins called CRAL_TRIO, which include yeast phosphatidylinositol transfer protein Sec14 and tocopherol transfer protein TTP. The crystal structure of human SPF at a resolution of 1.9 A reveals a two domain topology. The N-terminal 275 residues form a Sec14-like domain, while the C-terminal 115 residues consist of an eight-stranded jelly-roll barrel similar to that found in many viral protein structures. The ligand binding cavity has a peculiar horseshoe-like shape. Contrary to the Sec14 crystal structure, the lipid-exchange loop is in a closed conformation, suggesting a mechanism for lipid exchange.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carrier Proteins / chemistry*
  • Crystallography, X-Ray
  • Humans
  • Ligands
  • Lipid Metabolism
  • Lipoproteins / chemistry*
  • Models, Molecular
  • Protein Binding
  • Protein Conformation
  • Protein Structure, Tertiary
  • Spectrometry, Mass, Electrospray Ionization
  • Trans-Activators*


  • Carrier Proteins
  • Ligands
  • Lipoproteins
  • SEC14L2 protein, human
  • Trans-Activators

Associated data

  • PDB/106U