Structure of a synthetic fragment of the LALF protein when bound to lipopolysaccharide

Peptidic lipopolysaccharide (LPS) antagonists are the subject of intensive research. We report an NMR and modeling study of LALF-14 (GCKPTFRRLKWKYKCG), a synthetic cyclized fragment of the limulus anti-LPS factor (LALF) comprising residues 36-47. In a mixture with LPS we observed the transferred NOE effect and derived the LPS-bound structure of LALF-14. Neither the free nor the LPS-bound peptide displays NOEs indicative of a beta-sheet-like structure that is adopted by the fragment in the full-size protein. However, docking calculations show that the former structure is not a prerequisite for binding of LALF-14 to LPS.