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Crystal structure of saposin B reveals a dimeric shell for lipid binding.

Saposin B is a small, nonenzymatic glycosphingolipid activator protein required for the breakdown of cerebroside sulfates (sulfatides) within the lysosome. The protein can extract target lipids from membranes, forming soluble protein-lipid complexes that are recognized by arylsulfatase A. The crystal structure of human saposin B reveals an unusual shell-like dimer consisting of a monolayer of alpha-helices enclosing a large hydrophobic cavity. Although the secondary structure of saposin B is similar to that of the known monomeric members of the saposin-like superfamily, the helices are repacked into a different tertiary arrangement to form the homodimer. A comparison of the two forms of the saposin B dimer suggests that extraction of target lipids from membranes involves a conformational change that facilitates access to the inner cavity.

Pubmed ID: 12518053


  • Ahn VE
  • Faull KF
  • Whitelegge JP
  • Fluharty AL
  • PrivĂ© GG


Proceedings of the National Academy of Sciences of the United States of America

Publication Data

January 7, 2003

Associated Grants

  • Agency: NINDS NIH HHS, Id: NS31271

Mesh Terms

  • Amino Acid Sequence
  • Amino Acid Substitution
  • Binding Sites
  • Crystallography, X-Ray
  • Dimerization
  • Glycoproteins
  • Humans
  • Lipid Metabolism
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Structure, Secondary
  • Saposins
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Sphingolipid Activator Proteins