Biology subjects

Williams, G. J.

Publications and source records attributed to Williams, G. J..

5 recordsLinked to original sources

bioRxiv2026

Engineering the effector specificity of the macrolide-sensing transcription factor MphR for the detection of sesquiterpenes

Terpenes are a large, diverse class of natural products used as flavors, fragrances, pharmaceuticals, and more, yet obtaining them often requires either large quantities of biomass or complex chemical reactions. Directed evolution of key enzymes and pathways could improve biosynthetic yields, but most sesquiterpenes lack high-throughput screening methods to search large libraries of variants. To alleviate this bottleneck, we developed the first reported genetically encoded biosensor to detect four highly valuable sesquiterpenes: valencene, nootkatone, artemisinin, and cedrol. Starting with the macrolide transcription factor biosensor MphR, we screened a panel of mutants against the four sesquiterpenes, including MphR-13 (T17N/V18I/K21L/S106L/H147L/P161L), which readily detected all four sesquiterpenes. Computational modeling showed that the mutations reduced the size of the ligand-binding pocket compared with the wild type, which positively correlated with the biosensor's fluorescence output. Additionally, swapping the fluorescence reporter improved the sensor's response 15-20-fold, yielding a generalist sesquiterpene biosensor that can be further developed and applied to the directed evolution of sesquiterpene biosynthesis.

synthetic biology↗

bioRxiv2023

Cryo-EM structure of DDM1-HELLS chimera bound to nucleosome reveals a mechanism of chromatin remodeling and disease regulation

Human HELicase, Lymphoid Specific (HELLS), and plant homolog Deficient in DNA Methylation 1 (DDM1), belong to a distinct class of chromatin remodelers that play important roles in DNA repair, transcription, and maintenance of DNA methylation in heterochromatin. HELLS also promotes the growth of hard-to-treat cancers including glioblastoma and hepatocellular carcinoma. Here, we identify an auto-inhibitory HELLS N-terminal coiled-coil, unravelling a long-standing question of HELLS inactivity in vitro. Using cryo-EM, we determine the 3.5 [A] structure of an active DDM1-HELLS chimera in complex with a nucleosome. The structure reveals that a HELLS-specific insertion in the ATPase lobe 2 interacts with the nucleosome acidic patch to enhance chromatin remodeling. At the C-terminus, we resolve a unique motif, and disease hot spot, that binds and stabilizes the ATPase motor of the HELLS family of remodelers. Finally, we provide mechanistic insights for how post-translational modifications in the motor domain and midloop could modulate HELLS activity to regulate cancer stem cell state.

biochemistry↗

bioRxiv2023

ATM phosphorylates the FATC domain of DNA-PKcs at threonine 4102 to promote non-homologous end joining

Ataxia-telangiectasia mutated (ATM) drives the DNA damage response via modulation of multiple signal transduction and DNA repair pathways. Previously, ATM activity was implicated in promoting the non-homologous end joining (NHEJ) pathway to repair a subset of DNA double strand breaks (DSBs), but how ATM performs this function is still unclear. In this study, we identified that ATM phosphorylates the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), a core NHEJ factor, at its extreme C-terminus at threonine 4102 (T4102) in response to DSBs. Phosphorylation at T4102 stabilizes the interaction between DNA-PKcs and the Ku-DNA complex and promotes assembly and stabilization of the NHEJ machinery at DSBs. Ablating phosphorylation at this site results in decreased NHEJ, radiosensitivity, and increased radiation-induced genomic instability. Collectively, these findings establish a key role for ATM in NHEJ-dependent repair of DSBs through positive regulation of DNA-PKcs.

molecular biology↗

bioRxiv2020

Computationally-guided exchange of substrate selectivity motifs in a modular polyketide synthase acyltransferase

Acyltransferases (ATs) of modular polyketide synthases catalyze the installation of malonyl-CoA extenders into polyketide scaffolds. Subsequently, AT domains have been targeted extensively to site-selectively introduce various extenders into polyketides. Yet, a complete inventory of AT residues responsible for substrate selection has not been established, critically limiting the efficiency and scope of AT engineering. Here, molecular dynamics simulations were used to prioritize ~50 mutations in the active site of EryAT6 from erythromycin biosynthesis. Following detailed in vitro studies, 13 mutations across 10 residues were identified to significantly impact extender unit selectivity, including nine residues that were previously unassociated with AT specificity. Unique insights gained from the MD studies and the novel EryAT6 mutations led to identification of two previously unexplored structural motifs within the AT active site. Remarkably, exchanging both motifs in EryAT6 with those from ATs with unusual extender specificities provided chimeric PKS modules with expanded and inverted substrate specificity. Our enhanced understanding of AT substrate selectivity and application of this motif-swapping strategy is expected to advance our ability to engineer PKSs towards designer polyketides.

synthetic biology↗

bioRxiv2019

Red Sea SAR11 and Prochlorococcus Single-cell Genomes Reflect Globally Distributed Pangenomes

Evidence suggests many marine bacteria are cosmopolitan, with widespread but sparse strains poised to seed abundant populations upon conducive growth conditions. However, studies supporting this "microbial seed bank" hypothesis have analyzed taxonomic marker genes rather than whole genomes/metagenomes, leaving open the possibility that disparate ocean regions harbor endemic gene content. The Red Sea is isolated geographically from the rest of the ocean and has a combination of high irradiance, high temperature, and high salinity that is unique among the ocean; we therefore asked whether it harbors endemic gene content. We sequenced and assembled single-cell genomes of 21 SAR11 (subclades Ia, Ib, Id, II) and 5 Prochlorococcus (ecotype HLII) cells from the Red Sea and combined them with globally-sourced reference genomes to cluster genes into ortholog groups (OGs). Ordination of OG composition could distinguish clades, including phylogenetically cryptic Prochlorococcus ecotypes LLII and LLIII. Compared with reference genomes, 1% of Prochlorococcus and 17% of SAR11 OGs were unique to the Red Sea genomes (RS-OGs). Most (83%) RS-OGs had no annotated function, but 65% of RS-OGs were expressed in diel Red Sea metatranscriptomes, suggesting they could be functional. Searching Tara Oceans metagenomes, RS-OGs were as likely to be found as non-RS-OGs; nevertheless, Red Sea and other warm samples could be distinguished from cooler samples using the relative abundances of OGs. The results suggest that the prevalence of OGs in these surface ocean bacteria is largely cosmopolitan, with differences in population metagenomes manifested by differences in relative abundance rather than complete presence-absence of OGs.

microbiology↗