An amphipathic helical motif common to tumourolytic polypeptide NK-lysin and pulmonary surfactant polypeptide SP-B.
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.[1]References
- An amphipathic helical motif common to tumourolytic polypeptide NK-lysin and pulmonary surfactant polypeptide SP-B. Andersson, M., Curstedt, T., Jörnvall, H., Johansson, J. FEBS Lett. (1995) [Pubmed]
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