An amphipathic helical motif common to tumourolytic polypeptide NK-lysin and pulmonary surfactant polypeptide SP-B

FEBS Lett. 1995 Apr 10;362(3):328-32. doi: 10.1016/0014-5793(95)00268-e.


The tumour-lysing and antimicrobial polypeptide NK-lysin and the pulmonary surfactant-associated polypeptide SP-B exhibit 24% residue identities (49% similarities), including six half-cystine residues in the same disulphide bonding pattern, and similar far-UV circular dichroism spectra corresponding to 45-55% alpha-helix and 20-25% beta-sheet structures. From this, we conclude that the conformations of NK-lysin and SP-B are similar. In contrast, the functional properties of the two proteins are dissimilar: SP-B does not exhibit antibacterial activity and NK-lysin does not significantly effect phospholipid spreading at an air/water interface. Saposins, which solubilize lipids and activate lysosomal hydrolases, the pore-forming amoebapores, and parts of acid sphingomyelinase and acyloxyacylhydrolase, also share 18-27% sequence identities with NK-lysin (and SP-B), including the six conserved half-cystine residues. The inclusion of NK-lysin extends the family of saposin-like polypeptides, all members of which appear to interact with lipids. Strictly conserved structural features with implications for helix topology and lipid interactions are observed.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 1,2-Dipalmitoylphosphatidylcholine
  • Animals
  • Circular Dichroism
  • Escherichia coli / drug effects
  • Intestine, Small / chemistry
  • Micelles
  • Protein Structure, Secondary*
  • Proteolipids / chemistry*
  • Proteolipids / genetics
  • Proteolipids / pharmacology
  • Pulmonary Surfactants / chemistry*
  • Pulmonary Surfactants / genetics
  • Pulmonary Surfactants / pharmacology
  • Sequence Homology, Amino Acid
  • Surface Properties
  • Swine


  • Micelles
  • NK-lysin
  • Proteolipids
  • Pulmonary Surfactants
  • 1,2-Dipalmitoylphosphatidylcholine