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Glycan-mediated Functional Assembly of IL-1RI: Structural Insights into Completion of the Current Description for Immune Response
  • Maryam Azimzadeh Irani,
  • Mohammad Reza Ejtehadi
Maryam Azimzadeh Irani
Shahid Beheshti University
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Mohammad Reza Ejtehadi
Sharif University of Technology, Sharif University of Technology (SUT)
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Abstract

Interleukin 1 receptor type I (IL-1RI) is a transmembrane receptor that triggers the inflammatory response. Understanding its detailed mechanism of action is crucial for treating immune disorders. IL-1RI is activated upon the formation of its “functional assembly” that occurs by binding of the cytokine and the accessory protein (IL-1RAcP) to the receptor. Glycosylation of the IL-1RI and IL-1RAcP play critical roles in the activation process. Here, extensive classical and accelerated molecular dynamics simulations are carried out to examine the structural role of glycosylation in the arrangement of the functional assembly at the atomic level. It is shown that the assembly is built in two types of non-signalling and signalling forms with the latter being the most frequently occurring form. The non-signalling assembly is formed by binding of the compact conformation of the glycosylated IL-1RI to the IL-1RAcP. In this type of assembly, the IL-1R is not accessible to the cytokines and thus it is unable to send signals to the cell. The signalling assembly is formed by binding of the extended glycosylated IL-1RI to the accessory protein. This assembly is locked in the extended form by persistent hydrogen bonds within and between the interconnected glycans of IL-1RI and IL-1RAcP. Cytokine binding site of the IL-1RI extracellular domain is exposed in this type of assembly and the signals could be transported to the cell. Moreover, contrary to the experimental interpretations, in both types of the assembly, binding of the IL-1RAcP to IL-1RI is primary to the cytokine binding to the complex.