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Humayun Sharif trained as a structural biologist with Elena Conti at the Max Planck Institute of Biochemistry (Munich, Germany). He has MS (GIST, South Korea) and BS from (MAJU, Pakistan) in Bioinformatics. He is currently an instructor at Harvard Medical School/Boston Children’s Hospital with Hao Wu, following postdoctoral stints with Wu and Michael Eck at the same institution. He studies host-pathogen interaction and the innate immune response. He has a special interest in using structure-driven approaches for the elucidation of programmed cell-death pathways.
Inflammasomes are cytoplasmic supramolecular complexes that form in response to either microbial invasions or endogenous cell damage. Upon activation, inflammasomes initiate explosive programmed cell death (Pyroptosis). NLRP3 is one of the most studied inflammasome, but the molecular details of NLRP3 inflammasome activation remain elusive.
The study presented the cryo-electron microscopy (cryo-EM) structure of NLRP3 with NEK7 kinase and adenosine-dinucleotide (ADP) at 3.8 Å resolution. Structure determination by cryo-EM visualizes biomolecular assemblies in their native hydrated state at near atomic resolution due to the mechanical stability, low electron dose and image capture capabilities of modern detectors and electron microscopes. Associated advances in single-particle image processing algorithms allow assessment of structural heterogeneity over a large size range difficult to achieve by other methods. The size, heterogeneity, and flexibility of the NLRP3-NEK7 complex make cryo-EM the method of choice for its study.
Since NLRP3 is in an activated conformation in the complex, a homologous activated inflammasome structure was used for de novo modeling. This bipartite interaction of NEK7 with NLRP3-LRR in a disk-like assembly was revealed to be critical for activation. Almost all NLRP3 mutations lie in NACHT domain and surround the ADP-binding pocket. The structure rationalizes how these mutations compromise interdomain interactions of NACHT or disrupt the ADP-binding pocket required for NLRP3 activation. These insights were validated with subsequent biochemical and cellular assays. They will be valuable in guiding the design of inhibitors for treatment of CAPS and other inflammatory diseases.