DePaola, P. | bioRxiv Science

bioRxiv2022

Cryo-EM structure of amyloid fibril formed by α-synuclein familial A53E mutation

Synucleinopathies, including Parkinsons disease (PD), dementia with Lewy bodies (DLB), and multiple systems atrophy (MSA) have the same hallmark pathologic feature of misfolded -synuclein protein accumulation in the brain. PD patients who carry -syn hereditary mutations tend to have an earlier onset and more severe clinical symptoms and pathology than sporadic PD patients who carry wild-type (WT) -syn. Therefore, revealing the structural effect of -syn hereditary mutations on the wild-type fibril structure can help us understand synucleinopathies structural basis. Here, we present a 3.38 [A] cryo-electron microscopy structure of -synuclein fibrils containing the hereditary A53E mutation. The A53E fibril is symmetrically composed of two protofilaments, as are many other synucleopathic structures - including WT. Interestingly, the interface between the protofilaments in A53E has significantly less buried surface area than all other documented fibril structures of -syn and its other mutants. The A53E fibril also exhibits slower formation/growth in in vitro fibrillation experiment compared to other mutants. This implies that the structural differences - both in the protofilament and between each protofilament of A53E - change the aggregation mechanism, or in the least, its kinetics of formation. These differences influence the molecular characteristics of each fibril mutant and likely plays a macro-scale role in progressing one clinical pathology over another.

biophysics↗

bioRxiv2021

A phage parasite deploys a nicking nuclease effector to inhibit replication of its viral host

PLEs are phage parasites integrated into the chromosome of epidemic Vibrio cholerae. In response to infection by its viral host ICP1, PLE excises, replicates and hijacks ICP1 structural components for transduction. Through an unknown mechanism PLE prevents ICP1 from transitioning to rolling circle replication (RCR), a prerequisite for efficient packaging of the viral genome. Here, we characterize a PLE-encoded nuclease, NixI, that blocks phage development likely by nicking ICP1s genome as it transitions to RCR. NixI-dependent cleavage sites appear in ICP1s genome during infection of PLE(+) V. cholerae. Purified NixI demonstrates in vitro specificity for sites in ICP1s genome and NixI activity is enhanced by a putative specificity determinant co-expressed with NixI during phage infection. Importantly, NixI is sufficient to limit ICP1 genome replication and eliminate progeny production. We identify distant NixI homologs in an expanded family of putative phage satellites in Vibrios that lack nucleotide homology to PLEs but nonetheless share genomic synteny with PLEs. More generally, our results reveal a previously unknown mechanism deployed by phage parasites to limit packaging of their viral hosts genome and highlight the prominent role of nuclease effectors as weapons in the arms race between antagonizing genomes.

microbiology↗