Interferons type II and their receptors R1 and R2 in fish species: structure, function and evolution

Jiří Zahradník, Lucie Kolářová, Hana Pařízková, Petr Kolenko, and Bohdan Schneider

Laboratory of Biomolecular Recognition, Institute of Biotechnology of the Czech Academy of Sciences, v. v. i., BIOCEV, Průmyslová 595, CZ-252 42 Vestec, Czech Republic

Study of accessory cytokines and signaling pathways in fish provide important clues to understanding of evolution of the antiviral defense system in vertebrates. Interferon gamma (IFN-γ) is one of the key players in the regulation of immune system of vertebrates especially in response to viral infections. We studied phylogeny, biophysical and structural aspects of IFN-γ and its receptors in fish species to fill up the knowledge gap about its evolution and structural properties in fish species. In this study we determined the crystal structure of structure of IFN-γ from olive flounder (Paralichthys olivaceus, PoliIFN-γ) at 2.3 Å resolution. The overall fold of PoliIFN-γ is similar to the other known IFN-γ structures but significant differences were observed, namely the additional α-helix G at the C-terminus and a different angle between α-helices C and D. By comparing the known IFN-γ and structures of its two receptors R1 and R2 we suggest a putative structure of the binary and ternary complexes. Our computational analysis showed that three functionally tightly linked molecules, IFN-γ, IFN-γR1, and IFN-γR2, have probably underwent distinct evolutionary events. IFN-γ split into two distinct clusters of IFN-γ and IFN-γ related proteins. Genes for IFN-γ related proteins develop independently in different fish classes. Genes for IFN-γ receptor 1 also revealed the existence of two independently evolving receptor types. In contrast, there is no sign of existence of a second group of IFN-γ receptor 2.

Figure Three-dimensional (3D) structure of the IFN-γ dimer from Paralichthys olivaceus (PoliIFN-γ). A crystal structure of PDB entry 6F1E. The monomer 1 is shown in blue, the monomer 2 in white, the solvent accessible surface is shown in white.

This study was supported by the Czech Science Foundation grant 16-20507S and by the project New research methods to BIOCEV (CZ.1.05/2.1.00/19.0390) from the ERDF. It was conducted at the Institute of Biotechnology CAS with help of the institutional grant RVO 86652036. We thank HZB for the allocation of the synchrotron-radiation beamtime.