The first crystal structure of CD8αα from a cartilaginous fish

Zhao Jia; Jianhua Feng; Helen Dooley; Jun Zou; Junya Wang

doi:10.3389/fimmu.2023.1156219

The first crystal structure of CD8αα from a cartilaginous fish

Front Immunol. 2023 Apr 14:14:1156219. doi: 10.3389/fimmu.2023.1156219. eCollection 2023.

Authors

Zhao Jia^{1

2

3}, Jianhua Feng^{1

2

3}, Helen Dooley^{4

5}, Jun Zou^{1

2

3

6}, Junya Wang^{1

2

3}

Affiliations

¹ Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Ministry of Education, Shanghai Ocean University, Shanghai, China.
² International Research Center for Marine Biosciences, Ministry of Science and Technology, Shanghai Ocean University, Shanghai, China.
³ National Demonstration Center for Experimental Fisheries Science Education, Shanghai Ocean University, Shanghai, China.
⁴ Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD, United States.
⁵ Institute of Marine and Environmental Technology, Baltimore, MD, United States.
⁶ Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.

Abstract

Introduction: Cartilaginous fishes are the most evolutionary-distant vertebrates from mammals and possess an immunoglobulin (Ig)- and T cell-mediated adaptive immunity. CD8 is the hallmark receptor of cytotoxic T cells and is required for the formation of T cell receptor-major histocompatibility complex (TCR-MHC) class I complexes.

Methods: RACE PCR was used to obtain gene sequences. Direct dilution was applied for the refolding of denatured recombinant CD8 protein. Hanging-drop vapor diffusion method was performed for protein crystallization.

Results: In this study, CD8α and CD8β orthologues (termed ScCD8α and ScCD8β) were identified in small-spotted catshark (Scyliorhinus canicula). Both ScCD8α and ScCD8β possess an extracellular immunoglobulin superfamily (IgSF) V domain as in previously identified CD8 proteins. The genes encoding CD8α and CD8β are tandemly linked in the genomes of all jawed vertebrates studied, suggesting that they were duplicated from a common ancestral gene before the divergence of cartilaginous fishes and other vertebrates. We determined the crystal structure of the ScCD8α ectodomain homodimer at a resolution of 1.35 Å and show that it exhibits the typical topological structure of CD8α from endotherms. As in mammals, the homodimer formation of ScCD8αα relies upon interactions within a hydrophobic core although this differs in position and amino acid composition. Importantly, ScCD8αα shares the canonical cavity required for interaction with peptide-loaded MHC I in mammals. Furthermore, it was found that ScCD8α can co-immunoprecipitate with ScCD8β, indicating that it can form both homodimeric and heterodimeric complexes.

Conclusion: Our results expand the current knowledge of vertebrate CD8 dimerization and the interaction between CD8α with p/MHC I from an evolutionary perspective.

Keywords: CD8; MHC; T cells; cartilaginous fishes; evolution; shark; structure.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Biological Evolution
CD8 Antigens / metabolism
Fishes*
Histocompatibility Antigens Class I / genetics
Histocompatibility Antigens Class I / metabolism
Mammals
Recombinant Proteins / genetics
Vertebrates*

Substances

CD8 Antigens
Histocompatibility Antigens Class I
Recombinant Proteins

Grants and funding

This work is funded by the National Natural Science Foundation of China (Grant numbers: 32030112 and U21A20268) and Hunan Provincial Science and Technology Program (Grant number: 2021NK2025), China.