Neutrophils play a key role as primary phagocytic cells, because they constitute the first line of defense against bacterial invasion, and contribute to inflammatory processes. They migrate to infected and inflamed tissues along a concentration gradient of chemoattractant molecules. The N-formyltripeptide for-Met-Leu-Phe-OH (fMLP), a structural analog of bacterial metabolism products, and its methylester derivative for-Met-Leu-Phe-OMe (fMLP-OMe) are the reference compounds among chemotactic peptides. The binding of formylpeptide to its receptor leads to various coupling and uncoupling reactions involving the generation of second messengers and activation of effector enzymes. This signal transduction cascade leads to the activation not only of direction-specific movement (chemotaxis), but also a wide range of functions required for host defence, including the respiratory burst, phagocytosis, and lipid mediator synthesis.
The goal of the study herein reported is to clarify the features peculiar to the methionine receptor pocket. It as widely accepted that the L-Met residue seems to induce optimum chemotactic as well as secretory activities. The synthesized analogs, here reported, have clarified that the positively charged area in the Met pocket is (i) narrow in dimension, (ii) located at a well defined distance from the backbone, and (iii) oriented in a specific position, not completely surrounding the internally located said chain.
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