Mast cell and monocyte recruitment by S100A12 and Its Hinge Domain

Abstract

S100A12 is expressed at sites of acute, chronic, and allergic inflammation. S100 proteins have regions of high sequence homology, but the "hinge" region between the conserved calcium binding domains is structurally and functionally divergent. Because the murine S100A8 hinge domain (mS100A8 42-55) is a monocyte chemoattractant whereas the human sequence (hS100A843-56) is inactive, we postulated that common hydrophobic amino acids within the S100A12 hinge sequence may be functional. The hinge domain, S100A1238-53, was chemotactic for human monocytes and murine mast cells in vitro. S100A1238-53 provoked an acute inflammatory response similar to that elicited by S100A12 in vivo and caused edema and leukocyte and mast cell recruitment. Circular dichroism studies showed that S100A1238-53 had increased helical structure in hydrophobic environments. Mutations in S100A1238-53 produced using an alanine scan confirmed that specific hydrophobic residues (I44A, I47A, and I53A) on the same face of the helix were critical for monocyte chemotaxis in vitro and generation of edema in vivo. In a hydrophobic environment such as the cell membrane, these critical residues would likely align on one face of an α-helix to facilitate receptor interaction. Interaction is unlikely to occur via the receptor for advanced glycation end products but, rather, via a G-protein-coupled mechanism. © 2008 by The American Society for Biochemistry and Molecular Biology, Inc.