Elliott, P. R. | Search bioRxiv

bioRxiv2022

Sex-specific deubiquitylation drives immune-related neurodegeneration in Drosophila

Risk of neurodegenerative disease such as late onset Alzheimers is linked to aberrant ubiquitinylation and accumulation of non-degraded proteins in brain cells. A glial network of innate immune genes modulates inflammatory responses to such protein deposition. However, vulnerability differs between the sexes. Here, we show that the Drosophila homologue of the deubiquitylase Trabid can align the sex-specific aspects of neurodegenerative phenotypes with changes in ubiquitylation and inflammatory activity. An enzymatically null Trabid in flies, caused sex-specific changes in locomotion, sleep patterns, brain histology and ultimately, lifespan. These changes were underscored by altered ubiquitin and proteome enrichment profiles and the same enzymatic activity as its human counterpart. When the sex-determination gene transformer was silenced in astrocytes or immunocompetent tissues, sex differences were significantly reduced. Our results indicate that Trabid underscores sex-specificity in disease neurology, by controlling the balance between ubiquitylation and inflammation.

immunology↗

bioRxiv2022

Structural basis for antagonism of the ubiquitin ligase BIRC6 by SMAC

Apoptosis, a form of genetically programmed cell death, can be triggered by either internal or external signals ultimately activating caspases, a family of proteases1. Certain members of the inhibitors of apoptosis (IAP) family are sentinel proteins preventing untimely cell death by inhibiting caspases. IAPs are in turn regulated by antagonists including second mitochondria-derived activator of caspase (SMAC). Baculoviral IAP repeat-containing protein 6 (BIRC6), a giant IAP, possesses dual E2/E3 ubiquitin ligase activity and is implicated in apoptosis via caspase inhibition2-7. How this is achieved remains unknown. Here we show BIRC6 directly restricts activated caspase-3, and ubiquitinates activated caspases-3, -7 and -9 working exclusively with the non-canonical E1, UBA6. Importantly, we show SMAC supresses both mechanisms. Cryo-electron microscopy (cryo-EM) structures of BIRC6 alone and in complex with SMAC reveal BIRC6 exists as an anti-parallel dimer with a substrate-binding module juxtaposed to the catalytic domain at each end, and we identify multiple highly conserved unannotated domains important for architecture and function. Through our structural, biochemical and biophysical findings, we discover SMAC engages BIRC6 at multiple sites resulting in a sub-nanomolar affinity enabling SMAC to competitively displace caspases, thus antagonising BIRC6-mediated caspase inhibition.

biochemistry↗