Library · Biology & lab methods
What Heterologous Expression got wrong, from 19 theses
Summary written by a model from the records below: The records describe common obstacles encountered during heterologous expression, including protein insolubility, metabolic burden, and suboptimal yield. Engineered pathways frequently failed due to regulatory imbalances, improper host environments, or ineffective expression optimization strategies. These records come from graduate theses, 2021 to 2025, each labeled with its degree where the repository states it, and each links to its thesis. They were extracted by language models reading the full text, so treat each as a lead to read, not a verdict.
Plus 8 problems the authors left open, listed at the end.
Failure modes, by theses reporting them
Select a mode to jump to its records.
Recombinant proteins suffer from insolubility, misfolding, and poor expression
Recombinant proteins expressed in bacterial hosts aggregated into insoluble pellets or inclusion bodies, or suffered from misfolding that required host chaperones. Other attempts resulted in a total absence of detectable protein expression across different growth conditions and constructs.
Tried and failed
recombinant protein expression in bacterial host applied to heterologous eukaryotic transcription factors. Reason: complete lack of protein expression across multiple construct designs and growth conditions
Investigation of Protein Conformation With Novel Labeling Techniques Using Electron Paramagnetic Resonance Spectroscopy · Cornell · PhD
Tried and failed
recombinant protein expression in bacterial host applied to heterologous clostridial enzyme. Reason: the protein remained insoluble across all tested expression conditions
Using genomic context to enable metabolic discovery in industrially relevant Clostridia · Harvard · PhD
Tried and failed
recombinant protein expression and solubilization applied to heterologous full-length eukaryotic protein. Reason: insoluble protein aggregation in bacterial pellets
Investigating the Role of Drosophila Tomosyn in Synaptic Strength and Plasticity · MIT · PhD
Tried and failed
heterologous protein expression in bacterial host applied to biosynthetic tailoring enzymes. Reason: expressed wild-type enzyme and multiple homologs resulted in insoluble protein formation
Biosynthesis Guided the Discovery of Proteusin RiPP Natural Products · Georgia Tech · PhD
Considered and rejected
Considered and rejected: Rejected heterologous expression of HcgG in E. coli due to formation of insoluble inclusion bodies, switching to homologous expression in M. maripaludis.
Identification and characterization of two radical SAM enzymes involved in biosynthesis of the [Fe]-hydrogenase cofactor Identifizierung und Charakterisierung von zwei Radikal-SAM-Enzymen, die an der Biosynthese des [Fe]-Hydrogenase-Cofaktors beteiligt sind · University of Marburg · PhD
Carbon flux diversion and metabolic gaps result in poor target yields
Heterologous pathways often produced minimal or insufficient target titers despite successful genetic engineering and integration. Carbon flux was frequently diverted toward biomass, overflow products, or competing pathways rather than the desired compound.
Tried and failed
minimal-length metabolic pathway search and integration applied to heterologous biosynthesis of non-natural compounds. Reason: minimal pathways omitted necessary cosubstrate regeneration and integration with host metabolism, preventing feasible flux
Modeling, analysis, and design of complex biological networks · EPFL · PhD
Heterologous pathway expression causes severe metabolic burden and host toxicity
High pathway expression and multigene complexity imposed severe metabolic burden and growth inhibition, causing engineered strains to be outcompeted or to lose plasmids. Leaky expression or constitutive enzyme synthesis also triggered direct host toxicity and transcriptional silencing.
Tried and failed
heterologous biosynthetic gene cluster expression applied to bacterial natural product operons. Reason: leaky expression of the pathway caused severe host toxicity and cloning failure
Selective Elimination of Vibrio Pathogens via the Synergy of a Type Six Secretion System and a Natural Phenazine Antibiotic · Harvard · PhD
Tried and failed
adaptive laboratory evolution of heterologous metabolic pathways applied to nitrogen-fixing engineered bacteria. Outcome: worse than baseline. Reason: metabolic burden caused engineered strains to be outcompeted under non-selective nutrient-rich conditions
Directed evolution of nitrogenase · Imperial · PhD
Tried and failed
constitutive enzyme expression in multi-step metabolic pathways applied to heterologous biosynthetic pathway flux. Reason: causes severe metabolic burden, growth inhibition, and transcriptional silencing leading to zero product yield
Multiplexed transcriptional control strategies for biosynthesis from mixed substrates in Escherichia coli · MIT · PhD
Tried and failed
single-strain consolidation of multi-enzyme metabolic pathway applied to heterologous multi-step biosynthetic pathway expression. Outcome: no signal. Reason: metabolic burden and pathway complexity prevented detectable target molecule synthesis in monoculture
Development of engineered living material platforms for diverse applications in human and planetary health · UT Austin · PhD
Tried and failed
plasmid-based heterologous multi-enzyme pathway expression applied to bacterial metabolic engineering. Outcome: unstable. Reason: plasmid loss in liquid culture and insoluble protein expression prevented target metabolite production
Engineering the Skin Microbiome for Drug Delivery · Georgia Tech · PhD
Overexpression of pathway enzymes or regulators reduces product accumulation
Overexpressing downstream pathway enzymes, regulators, or precursor supply routes frequently backfired and lowered product titers. These interventions depleted essential pathway intermediates or suppressed the accumulation of target metabolites.
Tried and failed
co-expression of candidate biosynthetic enzymes applied to heterologous metabolic pathway reconstitution. Outcome: worse than baseline. Reason: candidate enzyme suppressed accumulation of target on-pathway intermediates
Elucidation of gene clusters underlying withanolide biosynthesis in ashwagandha · MIT · PhD
Tried and failed
concurrent overexpression of precursor supply pathway genes applied to heterologous metabolic pathway flux. Outcome: worse than baseline. Reason: overexpressing the citrate route decreased target polyketide biosynthesis
Developing Yarrowia lipolytica as a platform for polyketide production · UT Austin · PhD
Codon optimization and promoter engineering fail to improve expression
Codon optimization strategies depleted charged tRNA pools or eliminated reporter activation compared to native sequences. Similarly, selecting synthetic or native promoters resulted in weak expression or performed worse than alternative viral promoters.
Tried and failed
heterologous and synthetic promoter driving transgene expression applied to transgenesis in non-model insect embryos. Outcome: worse than baseline. Reason: Synthetic 3xP3 and Drosophila polyubiquitin promoters yielded poor expression compared to viral Hr5-IE1 promoter.
Building a molecular toolkit for gene editing and transgenesis in the farmed insect black soldier fly · Imperial · PhD
Tried and failed
host-specific codon optimization of heterologous transcription factor applied to heterologous transcriptional reporter activation in yeast. Outcome: worse than baseline. Reason: codon optimization reduced or eliminated fold-change activation compared to the native plant sequence
Synthetic Auxin Engineering: Building a Biofoundry Platform · Virginia Tech · Doctorate
Considered and rejected
Considered and rejected: Rejected relying on native promoters en masse for heterologous expression because they are relatively weak and conditionally expressed.
Natural products isolation from Trichoderma reesei · Leibniz Universität Hannover · PhD
Tried and failed
full codon optimization applied to heterologous protein expression yield. Outcome: worse than baseline. Reason: depletes charged optimal tRNA pools when recharging is rate-limiting, increasing cellular burden
Mechanistic modeling of gene expression dynamics in bacteria and phages · UT Austin · PhD
Non-native host environments fail to support protein assembly and enzymatic function
Transferring functional gene clusters into non-native bacterial hosts failed to confer expected enzymatic activity. Additionally, recombinant fusion proteins failed to assemble into extracellular crystals when expressed outside their native host strains.
Tried and failed
recombinant fusion protein crystal encapsulation applied to heterologous spore-forming bacterial expression systems. Outcome: did not generalise. Reason: fusion proteins failed to form extracellular crystals when expressed in non-native bacterial host strains
Spore-forming bacteria as pharmaceutical factories · Cambridge · PhD
Tried and failed
heterologous expression of functional gene cluster applied to bacterial host for metabolic complementation. Outcome: no signal. Reason: functional clusters from one host background failed to confer enzymatic activity when transferred to a different bacterium
Engineering plant-microbe communication for synthetic symbioses · MIT · PhD
Left open by the authors
Problems the authors named and did not get to.
Left open
Assay the expression levels and protein solubility of heterologous transcription factors expressed in Escherichia coli for biosensor development. Blocker: Requires a wet biology lab and protein expression/solubility experimental assays.
Multiplexed transcriptional control strategies for biosynthesis from mixed substrates in Escherichia coli · MIT · PhD
Left open
Perform heterologous expression of putative 17β-HSDH and A-ring reductase genes from E. lenta, R. gnavus, and Bacteroidetes to confirm biological function. Blocker: Requires a wet lab for molecular cloning, heterologous expression, and enzymatic assays
Gut bacterial metabolism of corticoids and other host-produced steroids · Harvard · PhD
Left open
Heterologously express AncD0, AncD1, or chimeric ancestral photosystem II reaction centre proteins in a model host organism. Blocker: Requires wet lab molecular biology and biochemical apparatus for heterologous expression and protein characterization.
Bioinformatic and bioenergetic studies on the evolution of photosystem II · Imperial · PhD
Left open
Express E. coli SSB and nuclear-targeted human SSBP1/SSBP2 in mammalian cells and yeast to test for enhanced NHEJ repair. Blocker: Requires a wet-lab environment for molecular cloning, heterologous protein expression, and mammalian/yeast cell culture assays.
Enhanced Genomic Stability and its Effects on Aging and the Epigenome · Harvard · PhD
Left open
Evaluate polyprotein expression or alternative heterologous nitrogenase clusters from other diazotrophs in E. coli. Blocker: Requires wet lab genetic engineering, strain cultivation, and biochemical evaluation.
Directed evolution of nitrogenase · Imperial · PhD
Left open
Experimentally characterize the 72 plantiSMASH-predicted plant biosynthetic gene clusters identified in kratom. Blocker: Requires wet-lab synthesis, cloning, and heterologous expression in yeast or physical plant assays
Multiplex Plant Biosynthetic Pathway Integration and Gene Discovery in Saccharomyces Cerevisiae · Cornell · PhD
Left open
Elucidate the chemical structures and biosynthetic mechanisms of predicted polyketides, non-ribosomal peptides, and terpene synthases from phycosphere metagenomic genomes. Blocker: Requires wet-lab experimental validation, heterologous expression, isolation, and analytical structural characterization (NMR/MS).
Novel microbes and viruses with roles in biogeochemical cycling and eukaryogenesis in marine systems · UT Austin · PhD
Left open
Determine if the C-terminal domain of SpyCEP exhibits in vivo biological activity via heterologous expression in L. lactis. Blocker: Requires a wet lab, recombinant protein expression in L. lactis, and in vivo biological assays.
Targeting the streptococcal virulence factor SpyCEP as a novel therapeutic approach · Imperial · PhD
Who has worked on this
Authors of the public theses cited on this page, most-cited first.
- Emily Bennett · Imperial · PhD · 2023
Directed evolution of nitrogenase - Cynthia Ni · MIT · PhD · 2022
Multiplexed transcriptional control strategies for biosynthesis from mixed substrates in Escherichia coli - Sarah Beth Bier · Harvard · PhD · 2025
Selective Elimination of Vibrio Pathogens via the Synergy of a Type Six Secretion System and a Natural Phenazine Antibiotic - Erin E. Reynolds · MIT · PhD · 2025
Elucidation of gene clusters underlying withanolide biosynthesis in ashwagandha - James Daniel Fawcett · Imperial · PhD · 2024
Building a molecular toolkit for gene editing and transgenesis in the farmed insect black soldier fly - Duncan James Kountz · Harvard · PhD · 2024
Using genomic context to enable metabolic discovery in industrially relevant Clostridia - John Alexander Jr. Bryant · Virginia Tech · Doctorate · 2024
Synthetic Auxin Engineering: Building a Biofoundry Platform - Franklin Gong · Cornell · PhD · 2023
Multiplex Plant Biosynthetic Pathway Integration and Gene Discovery in Saccharomyces Cerevisiae - Robert Dunleavy · Cornell · PhD · 2023
Investigation of Protein Conformation With Novel Labeling Techniques Using Electron Paramagnetic Resonance Spectroscopy - Nguyet Nguyen · Georgia Tech · PhD · 2023
Biosynthesis Guided the Discovery of Proteusin RiPP Natural Products - Veronica Montgomery · Georgia Tech · PhD · 2023
Engineering the Skin Microbiome for Drug Delivery - Megan D. McCurry · Harvard · PhD · 2023
Gut bacterial metabolism of corticoids and other host-produced steroids
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