The annexin I sequence gln(9)-ala(10)-trp(11)-phe(12) is a core structure for interaction with the formyl peptide...

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, Gln(9)-Lys(25), is mediated by FPR1, a member of the formyl peptide receptor family expressed in human neutrophils. To determine the core structure in Gln(9)-Lys(25), smaller peptides were generated, and their capacity to activate neutrophils was determined. A peptide spanning from amino acid Glu(14) to Lys(25) was inactive, whereas the activity was retained in the Gln(9)-Tyr(20) peptide. Removal of amino acids from the C and N terminus of Gln(9)-Tyr(20) revealed that the first amino acid (Gln(9)) was of the utmost importance for activity. The core structure that activated the neutrophil NADPH oxidase to release superoxide anions was Gln(9)-Ala(10)-Trp(11)-Phe(12). 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 Gln(9)-Phe(12) 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.