Biology subjects

Jiang, F.

Publications and source records attributed to Jiang, F..

93 records · Page 6Linked to original sources

bioRxiv2018

Temperature-responsive competitive inhibition of CRISPR-Cas9

CRISPR-Cas immune systems utilize RNA-guided nucleases to protect bacteria from bacteriophage infection. Bacteriophages have in turn evolved inhibitory anti-CRISPR (Acr) proteins, including six inhibitors (AcrIIA1-6) that can block DNA cutting and genome editing by type II-A CRISPR-Cas9 enzymes. We show here that AcrIIA2 and its homologue, AcrIIA2b, prevent Cas9 binding to DNA by occluding protein residues required for DNA binding. Cryo-EM-determined structures of AcrIIA2 or AcrIIA2b bound to S. pyogenes Cas9 reveal a mode of competitive inhibition of DNA binding that is distinct from other known Acrs. Differences in the temperature dependence of Cas9 inhibition by AcrIIA2 and AcrIIA2b arise from differences in both inhibitor structure and the local inhibitor-binding environment on Cas9. These findings expand the natural toolbox for regulating CRISPR-Cas9 genome editing temporally, spatially and conditionally.

biochemistry↗

bioRxiv2018

Small-scale soil microbial community heterogeneity linked to landforms on King George Island, maritime Antarctica

We analysed soil-borne microbial (bacterial, archaeal, and fungal) communities around the Fildes Region of King George Island, maritime Antarctica, which were divided into two groups according to soil elemental compositions and environmental attributes (soil chemical parameters and vegetation conditions) located in Holocene raised beach and Tertiary volcanic stratigraphy. Prokaryotic communities of the two groups were well separated; they predominantly correlated with soil elemental compositions, and were secondly correlated with environmental attributes (e.g., soil pH, total organic carbon, [Formula], and vegetation coverage; Pearson test, r = 0.59 vs. 0.52, both P < 0.01). The relatively high abundance of P, S, Cl, and Br in Group 1 was likely due to landform uplift. Lithophile-elements (Si, Al, Ca, Sr, Ti, V, and Fe) correlated with prokaryotic communities in Group 2 may originate from weathering of Tertiary volcanic rock. The elements and nutrients accumulated during formation of different landforms influenced the development of soils, plant growth, and microbial communities, and resulted in small-scale spatially heterogeneous biological distributions. We propose that the geological evolution of the Fildes Region was crucial to its microbial community development.\n\nIMPORTANCEThis current study analyzed soil-borne microbial communities around the Fildes Region of King George Island, maritime Antarctica, which were divided into two groups according to soil elemental compositions and environmental attributes. We provide new evidence for the crucial influence of landforms on small-scale structures and spatial heterogeneity of soil microbial communities.

microbiology↗

bioRxiv2017

Disabling Cas9 by an anti-CRISPR DNA mimic

CRISPR-Cas9 gene editing technology is derived from a microbial adaptive immune system, where bacteriophages are often the intended target. Natural inhibitors of CRISPR-Cas9 enable phages to evade immunity and show promise in controlling Cas9-mediated gene editing in human cells. However, the mechanism of CRISPR-Cas9 inhibition is not known and the potential applications for Cas9 inhibitor proteins in mammalian cells has not fully been established. We show here that the anti-CRISPR protein AcrIIA4 binds only to assembled Cas9-single guide RNA (sgRNA) complexes and not to Cas9 protein alone. A 3.9 [A] resolution cryo-EM structure of the Cas9-sgRNA-AcrIIA4 complex revealed that the surface of AcrIIA4 is highly acidic and binds with 1:1 stoichiometry to a region of Cas9 that normally engages the DNA protospacer adjacent motif (PAM). Consistent with this binding mode, order-of-addition experiments showed that AcrIIA4 interferes with DNA recognition but has no effect on pre-formed Cas9-sgRNA-DNA complexes. Timed delivery of AcrIIA4 into human cells as either protein or expression plasmid allows on-target Cas9-mediated gene editing while reducing off-target edits. These results provide a mechanistic understanding of AcrIIA4 function and demonstrate that inhibitors can modulate the extent and outcomes of Cas9-mediated gene editing.

biochemistry↗