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Speight, R.

Publications and source records attributed to Speight, R..

6 recordsLinked to original sources

Evaluating the cross-species transferability and scaling of sequence-to-function predictions in AlphaGenome

Deep learning models that predict molecular phenotypes directly from DNA sequence offer a powerful framework for interpreting genomic variation. Recently, AlphaGenome was introduced as a deep sequence-to-function architecture capable of predicting observations that historically required experiments. While the model has shown high accuracy, it was primarily evaluated on human variants scored against a reference genome. Here, we test performance on mouse data, the other species AlphaGenome was trained on although with fivefold fewer features than human (1,128 versus 5,930). We demonstrate that AlphaGenomes predictive performance varies considerably depending on the functional task. Specifically, predicted quantitative expression effects are directionally weak and compressed roughly 100-fold relative to empirical benchmarks across both reconstructed-haplotype and single-variant regimes. In contrast, canonical splice-site disruptions are recognized with near-identical accuracy in mouse and human (AUC 0.96 versus 0.98), displaying no cross-species divergence in predicted effect magnitude. We developed a scoring-approach for AI-agents to autonomously assess AlphaGenome prediction confidence and accurately differentiate between AlphaGenomes robust sequence-level recognition across species and its current limitations when interpreting un-fine-mapped regulatory variants. This demonstrates how GenAI innovations that are still under development can safely be harnessed by wrapping a responsible AI layer around the call to intercept flawed results, thereby adhering to international standards, such as the Australian Voluntary AI Safety Standard (VAISS).

bioinformatics↗

Co-Substrate Free Valorisation of Lignin Monomers by Assimilation of C1 and C2 By-Products

Lignin is an underutilised global resource with significant potential for the production of chemicals that are currently derived from fossil resources. However, biotechnological lignin valorisation faces various challenges including its recalcitrance and the toxicity of aromatic intermediates, products, and by-products like formaldehyde. While biochemical production from lignin-derived monomers has been demonstrated by disrupting native lignin degradation pathways, this approach required co-feeding additional carbon sources such as glucose for growth. This dependence on additional carbon sources can create competition with the food industry and undermine the economic sustainability of the bioprocess. Here, we report growth of a protocatechuate production strain of Pseudomonas putida EM42 on the by-products from p-coumarate and ferulate valorisation, achieving carbon efficiencies of up to 78 %. Additional flux balance analysis identified C1 assimilation pathways, including two novel pathways, beneficial for the growth on the formaldehyde by-product from ferulate degradation leading to improved carbon utilisation. This study demonstrates how by-product utilisation from lignin conversion can eliminate the need for co-feeding additional carbon sources, thereby potentially improving the efficiency of lignin valorisation.

bioengineering↗

Cyanamide-inducible expression of homing nuclease I-SceI for iterative genome engineering and parallel promoter characterisation in Saccharomyces cerevisiae

In synthetic biology, microbial chasses including yeast Saccharomyces cerevisiae are iteratively engineered with increasing complexity and scale. Wet-lab genetic engineering tools are developed and optimised to facilitate strain construction but are often incompatible with each other due to shared regulatory elements, such as the galactose-inducible (GAL) promoter in S. cerevisiae. Here, we prototyped the cyanamide-induced I-SceI-mediated double-strand DNA breaks (DSBs) for selectable marker recycling in yeast metabolic engineering. We further combined cyanamide-induced I-SceI-mediated DSB and maltose-induced MazF-mediated negative selection for plasmid-free in situ promoter replacement, which simplified the molecular cloning procedure for promoter characterisation in S. cerevisiae. We then characterised three tetracycline-inducible promoters of differential strength, a non-leaky {beta}-estradiol-inducible promoter, cyanamide-inducible DDI2 promoter, bidirectional MAL32/MAL31 promoters, and five pairs of bidirectional GAL1/GAL10 promoters. Overall, alternative regulatory controls for genome engineering tools are important for the construction of complexed genotypes in microbial systems for synthetic biology and metabolic engineering applications.

synthetic biology↗

The integration of tandem gene repeats via a bacterial type-II toxin-antitoxin-mediated gene amplification (ToxAmp) system and stability visualisation in Saccharomyces cerevisiae

Tandem gene repeats naturally occur as important genomic features and determine many traits in living organisms, like human diseases and microbial productivities of target bioproducts. Here, we develop a bacterial type-II toxin-antitoxin-mediated method to manipulate genomic integration of tandem gene repeats in Saccharomyces cerevisiae and further visualise the evolutionary trajectories of gene repeats. We designed a tri-vector system to introduce toxin-antitoxin-driven gene amplification (ToxAmp) modules, and accidentally re-visited the high-level capacity of multi-fragment co-transformation in S. cerevisiae. This system delivered the multi-copy gene integration in the form of tandem gene repeats spontaneously and independently from toxin-antitoxin-mediated selection. Inducing the toxin (RelE) expressing via a copper (II)-inducible CUP1 promoter successfully drove the in-situ gene amplification of the antitoxin (RelB) module, resulting in [~]40 copies of a green fluorescence reporter (GFP) gene per copy of genome. The copy-number changes, increasing and decreasing, and stable maintenance were visualised using the GFP and blue chromoprotein AeBlue as reporters. Copy-number increasing happened spontaneously not depending on a selection pressure and was quickly enriched through toxin-antitoxin-mediated selection. In summary, the bacterial toxin-antitoxin systems provide a flexible mechanism to manipulate gene copy number in eukaryotic cells and can be exploited for synthetic biology and metabolic engineering applications. Table of Contents Graphic O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=146 SRC="FIGDIR/small/578080v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@75d1f3org.highwire.dtl.DTLVardef@12aafeforg.highwire.dtl.DTLVardef@184a1a5org.highwire.dtl.DTLVardef@90586a_HPS_FORMAT_FIGEXP M_FIG C_FIG

synthetic biology↗

Active site mutations of F420-dependent alkene reductases reverse stereoselectivity

Ene-reductases from the Flavin/Deazaflavin Oxidoreductase (FDOR) family have potential value in biocatalysis as they typically exhibit complementary stereoselectivity to the widely utilized Old Yellow Enzyme (OYE) family, yet they are comparatively poorly understood at a mechanistic level. Here, we use a rational design approach to generate a library of 46 active site mutants of two FDORs from Mycobacterium smegmatis and examine the effects on conversion and stereoselectivity against a panel of substrates. Analysis of the effects of these mutations on stereoselectivity across all substrates revealed that the catalytic mechanism is highly sensitive to the polarity of the immediate active site. A conserved active site tyrosine in these enzymes, which does not serve as the proton donor, strongly affects stereochemical outcomes with C- (but not C{beta}-) substituted substrates. Notably, a Tyr-Met mutation at this position reversed the diastereomeric excess (de) with (R)-carvone from 85.3% to -17.3% (cis/trans). Additionally, this mutation significantly increases activity with (1S)- verbenone. Finally, we show that the altered stereoselectivity is not due to a "flipped" substrate binding mode in these mutants, but rather that the hydrogenation mode is altered to favor syn relative to anti addition. These results show that the FDORs are highly engineerable and that, despite their superficial similarity, the OYE and FDOR families differ in crucial mechanistic aspects.

synthetic biology↗

Asymmetric ene-reduction of α,β-unsaturated compounds by F420-dependent oxidoreductases A (FDOR-A) enzymes from Mycobacterium smegmatis

The stereoselective reduction of alkenes conjugated to electron-withdrawing groups by ene-reductases has been extensively applied to the commercial preparation of fine chemicals. Although several different enzyme families are known to possess ene-reductase activity, the Old Yellow Enzyme (OYE) family has been the most thoroughly investigated. Recently, it was shown that a subset of ene-reductases belonging to the flavin/deazaflavin oxidoreductase (FDOR) superfamily exhibit enantioselectivity that is generally complementary to that seen in the OYE family. These enzymes belong to one of several FDOR subgroups that use the unusual deazaflavin cofactor F420. Here, we explore several enzymes of the FDOR-A subgroup, characterizing their substrate range and enantioselectivity, including the complete conversion of both isomers of citral to (R)-citronellel with 99% ee. Protein crystallography combined with computational docking has allowed the observed stereoselectivity to be mechanistically rationalized for two enzymes. These findings add further support for the FDOR and OYE families of ene-reductases being generally stereocomplementary to each other and highlight their potential value in asymmetric ene-reduction.

biochemistry↗