The Annexin I Sequence Gln9-Ala10-Trp11-Phe12 Is a Core Structure for Interaction with the Formyl Peptide Receptor 1

The N-terminal part of the calcium-regulated and phospholipid-binding protein annexin AI contains peptide sequences with pro- and anti-inflammatory activities. We have earlier shown that a proinflammatory signal triggered by one of these peptides, Gln9–Lys25, is mediated by FPR1, a member of the formyl peptide receptor family expressed in human neutrophils. To determine the core structure in Gln9–Lys25, smaller peptides were generated, and their capacity to activate neutrophils was determined. A peptide spanning from amino acid Glu14 to Lys25 was inactive, whereas the activity was retained in the Gln9–Tyr20 peptide. Removal of amino acids from the C and N terminus of Gln9–Tyr20 revealed that the first amino acid (Gln9) was of the utmost importance for activity. The core structure that activated the neutrophil NADPH oxidase to release superoxide anions was Gln9-Ala10-Trp11-Phe12. This peptide also inhibited the activity induced by N-formyl-Met-Leu-Phe and WKYMVM. A structural model of the peptide agonist-FPR1 complex suggests that the transmembrane part of the binding pocket of the receptor binds optimally to a tetrapeptide. According to the model and the results presented, the N-terminal amino acid glutamine in Gln9–Phe12 is located close to the bottom of the binding cleft, leaving for steric reasons insufficient space to extend the peptide at the N terminus. The addition of amino acids at the C terminus will not affect binding. The model presented may be helpful in developing specific FPR1 ligands.