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Published on: March 5, 2018
Structure of the caspase-recruitment domain from a zebrafish guanylate-binding protein
Tengchuan Jin1, Mo Huang, Patrick Smith
1Structural Immunobiology Unit, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 4 Memorial Drive, Building 4, Room 228, Bethesda, MD 20892-0430, USA.
Insights
The caspase-recruitment domain (CARD) in zebrafish interferon-induced guanylate-binding protein 1 (zIGBP1) adopts a six-helix bundle fold. This structure, similar to mammalian inflammasome proteins, reveals charged patches potentially mediating protein interactions.
Area of Science:
- Structural Biology
- Immunology
- Zebrafish models
Background:
- Caspase-recruitment domains (CARDs) are crucial for innate immune signaling complex assembly, like inflammasomes.
- Mammalian CARD structures are known, but structural data from other organisms are lacking.
- The zebrafish interferon-induced guanylate-binding protein 1 (zIGBP1) possesses a CARD domain.
Purpose of the Study:
- To determine the three-dimensional structure of the zebrafish zIGBP1 CARD domain.
- To compare the zIGBP1 CARD structure with known mammalian CARD structures.
- To identify potential interaction surfaces on the zIGBP1 CARD.
Main Methods:
- X-ray crystallography was used to determine the structure of the zIGBP1 CARD fused with maltose-binding protein.
- The structure was resolved at a resolution of 1.47 Å.
- Analysis of surface charge distribution was performed.
Main Results:
- The zIGBP1 CARD exhibits a six-helix bundle fold, characteristic of the death-domain superfamily.
- A bent α1 helix, common to known CARD structures, was observed.
- Distinct positively and negatively charged patches were identified on the zIGBP1 CARD surface.
Conclusions:
- The zIGBP1 CARD shares structural homology with mammalian CARDs, particularly NLRP1.
- The identified charged patches may play a role in mediating interactions with partner proteins.
- Further functional studies are needed to elucidate the physiological role of zIGBP1 in zebrafish immunity.
Abstract:
The caspase-recruitment domain (CARD) mediates homotypic protein-protein interactions that assemble large oligomeric signaling complexes such as the inflammasomes during innate immune responses. Structural studies of the mammalian CARDs demonstrate that their six-helix bundle folds belong to the death-domain superfamily, whereas such studies have not been reported for other organisms. Here, the zebrafish interferon-induced guanylate-binding protein 1 (zIGBP1) was identified that contains an N-terminal GTPase domain and a helical domain typical of the mammalian guanylate-binding proteins, followed by a FIIND domain and a C-terminal CARD similar to the mammalian inflammasome proteins NLRP1 and CARD8. The structure of the zIGBP1 CARD as a fusion with maltose-binding protein was determined at 1.47 Å resolution. This revealed a six-helix bundle fold similar to the NLRP1 CARD structure with the bent α1 helix typical of all known CARD structures. The zIGBP1 CARD surface contains a positively charged patch near its α1 and α4 helices and a negatively charged patch near its α2, α3 and α5 helices, which may mediate its interaction with partner domains. Further studies using binding assays and other analyses will be required in order to address the physiological function(s) of this zebrafish protein.
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