Crystal structure of caspase-11 CARD provides insights into caspase-11 activation

Muziying Liu,Tengchuan Jin,Xiaocong Cao,Ayesha Zahid,Sicheng Fu,Huan Ma,Rongbin Zhou,Zhihao Xu,Kang Zhou,Xueying Yin,Ying Zhou,Li Bai,Xiaodong Ye,Weihong Zeng,Kang Ni

doi:10.1038/s41421-020-00201-w

Abstract

Murine caspase-11 is the centerpiece of the non-canonical inflammasome pathway that can respond to intracellular LPS and induce pyroptosis. Caspase-11 contains two components, an N-terminal caspase recruitment domain (CARD) and a C-terminal catalytic domain. The aggregation of caspase-11 is thought to promote the auto-processing and activation of caspase-11. However, the activation mechanism of caspase-11 remains unclear. In this study, we purified the caspase-11 CARD fused to an MBP tag and found it tetramerizes in solution. Crystallographic analysis reveals an extensive hydrophobic interface formed by the H1–2 helix mediating homotypic CARD interactions. Importantly, mutations of the helix H1–2 hydrophobic residues abolished the tetramerization of MBP-tagged CARD in solution and failed to induce pyroptosis in cells. Our study provides the first evidence of the homotypic interaction mode for an inflammatory caspase by crystal model. This finding demonstrates that the tetramerization of the N-terminal CARD can promote releasing of the catalytic domain auto-inhibition, leading to the caspase-11 activation.

Highlights

Inflammasome signaling pathways sense different body injuries and pathogen infections, and are essential components of the innate immune system[1]
Unlike several NOD-like receptors (NLRs) and AIM2-like receptors (ALRs) that, in response to certain Pathogen Associated Molecular Pattern (PAMPs), form a canonical inflammasome complex for activation caspase-1, the noncanonical pathway can directly respond to the cytosolic bacterial lipopolysaccharide (LPS), a molecule that plays an important role in endotoxic shock[2,3,4,5,6,7,8]
maltose-binding protein (MBP)-tagged caspase-11 caspase recruitment domain (CARD) exists as tetramers in solution The functional motif of caspase-11 CARD is reported to reside in amino acid residues 1–59 of caspase-11 protein[11], the canonical CARD region is predicted to be within residues 1–80

Summary

Introduction

Inflammasome signaling pathways sense different body injuries and pathogen infections, and are essential components of the innate immune system[1]. Unlike several NOD-like receptors (NLRs) and AIM2-like receptors (ALRs) that, in response to certain Pathogen Associated Molecular Pattern (PAMPs), form a canonical inflammasome complex for activation caspase-1, the noncanonical pathway can directly respond to the cytosolic bacterial lipopolysaccharide (LPS), a molecule that plays an important role in endotoxic shock[2,3,4,5,6,7,8]. Murine caspase-11 and its human orthologs caspase-4/5 are essential for the non-canonical inflammasome pathway[9]. Caspase-11, -4, and -5 belong to a family of aspartatespecific cysteine proteases. Caspase-11, -4, and -5 contain an N-terminal death fold named caspase recruitment domain (CARD) and a C-terminal catalytic domain[14]

Methods

Results

Conclusion