The human innate immune system is composed of several components that work in conjunction to curtail pathogenesis. As a well-established member of the innate immune system, S100A12 is known to conduct antimicrobial activities via sequestration of zinc ions. This sequestration limits the pathogen's access to Zn2+, a critical nutrient for their proliferation. Furthermore, during infection, S100A12 interacts with membrane receptors such as the receptor for advanced glycation end products (RAGE) to initiate a pro-inflammatory signaling cascade. Although known to participate in both antimicrobial and pro-inflammatory activities, the mode of interaction of S100A12, particularly with the membrane receptors, is not known. Our goal in this proposal is to characterize the metal binding properties of S100A12 that allow it to perform antimicrobial activities and develop an atomic scale understanding of interaction of S100A12 with RAGE. We propose that this interaction is initiated by its antimicrobial activities allowing us to hypothesize that the antimicrobial and pro- inflammatory activities of S100A12 are interdependent. Our studies demonstrate that by the antimicrobial activity of Zn2+ sequestration, S100A12 undergoes self- assembly leading to the formation of oligomers. We also show that this self-assembly is dependent on the concentration of S100A12. These results, in conjunction with reports in the literature demonstrating the presence of oligomeric S100A12 species in blood serum and human tissues, have allowed us to propose a scheme describing the role of S100A12 in the immune system. This model proposes S100A12 concentration dependent pro-inflammatory actions in cells that are initiated upon its antimicrobial responses, thereby establishing a correlation between its antimicrobial and pro-inflammatory activities. To test our hypothesis, we propose the following specific aims to characterize S100A12 antimicrobial functions and the role of its oligomers: (i) characterization of the coordination environment of transition metal ions in oligomeric S100A12 assemblies; (ii) identification of the mechanism of oligomerization of S100A12; and (iii) determination of the dependence of the mode of interaction of S100A12 with RAGE and the order of oligomerization. These proposed studies will provide atomic- and molecular-level snapshots of the S100A12-RAGE interactions in vitro, which will provide guidance for the mode of the interaction between these cellular components in vivo. In line with our long-term goal to unravel atomistic details of metal-dependent processes in the human immune response, this proposal will provide insights into the role of metal dependent self- assembly of S100A12. These studies will enhance the understanding of the functioning of S100A12 and provide basis for the design of novel therapeutics.
Human cells combat pathogenic attack by activating the innate immune response, which performs antimicrobial and pro-inflammatory activities. This proposed study aims to identify molecular-level interactions between the components of the innate immune system that curtail virulence and initiate inflammation. Elucidating the mode of such interactions is critical for the understanding of the human immune system and for the development of efficient therapeutics to inhibit pathogenesis.
