Hal S Alper

University of Texas at Austin, Austin, Texas, United States

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Publications (66)406.72 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The complete biosynthetic replacement of petroleum transportation fuels requires a metabolic pathway capable of producing short chain n-alkanes. Here, we report and characterize a proof-of-concept pathway that enables microbial production of the C5n-alkane, pentane. This pathway utilizes a soybean lipoxygenase enzyme to cleave linoleic acid to pentane and a tridecadienoic acid byproduct. Initial expression of the soybean lipoxygenase enzyme within a Yarrowia lipolytica host yielded 1.56mg/L pentane. Efforts to improve pentane yield by increasing substrate availability and strongly overexpressing the lipoxygenase enzyme successfully increased pentane production three-fold to 4.98mg/L. This work represents the first-ever microbial production of pentane and demonstrates that short chain n-alkane synthesis is conceivable in model cellular hosts. In this regard, we demonstrate the potential pliability of Y. lipolytica towards the biosynthetic production of value-added molecules from its generous fatty acid reserves.
    Journal of Biotechnology 04/2013; · 3.18 Impact Factor
  • Leqian Liu, Heidi Redden, Hal S Alper
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    ABSTRACT: Microbial systems provide an attractive, renewable route to produce desired organic molecules such as fuels and chemicals. While attention within the field of metabolic engineering has mostly focused on Escherichia coli, yeast is a potent host and growing host for industrial products and has many outstanding, biotechnologically desirable native traits. Thus, there has been a recent shift in focus toward yeast as production hosts to replace E. coli. As such, products have diversified in yeast beyond simply ethanol. Additionally, nonconventional yeasts have been considered to move beyond Saccharomyces cerevisiae. This review highlights recent advances in metabolic engineering of yeasts for producing value-added chemical compounds including alcohols, sugar derivatives, organic acids, fats, terpenes, aromatics, and polyketides. Furthermore, we will also discuss the future direction of metabolic engineering of yeasts.
    Current Opinion in Biotechnology 03/2013; · 8.04 Impact Factor
  • Amanda M Lanza, Do Soon Kim, Hal S Alper
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    ABSTRACT: Selection markers are common genetic elements used in recombinant cell line development. While several selection systems exist for use in mammalian cell lines, no previous study has comprehensively evaluated their performance in the isolation of recombinant populations and cell lines. Here we examine four antibiotics, hygromycin, neomycin, puromycin, and Zeocin, and their corresponding selector genes, using a green fluorescent protein (GFP) as a reporter in two model cell lines, HT1080 and HEK293. We identify Zeocin as the best selection agent for cell line development in human cells. In comparison to the other selection systems, Zeocin is able to identify populations with higher fluorescence levels, which in turn leads to the isolation of better clonal populations and less false positives. Further, Zeocin-resistant populations exhibit better transgene stability in the absence of selection pressure compared to other selection agents. All isolated Zeocin-resistant clones, regardless of cell type, exhibited GFP expression. By comparison, only 79% of hygromycin-resistant, 47% of neomycin-resistant and 14% of puromycin-resistant clones expressed GFP. Based on these results, we would rank Zeocin > hygromycin ∼ puromycin > neomycin for cell line development in human cells. Furthermore, this study demonstrates that selection marker choice does impact cell line development.
    Biotechnology Journal 03/2013; · 3.71 Impact Factor
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    ABSTRACT: The dicarboxylic acid muconic acid has garnered significant interest due to its potential use as a platform chemical for the production of several valuable consumer bio-plastics including nylon-6,6 and polyurethane (via an adipic acid intermediate) and polyethylene terephthalate (PET) (via a terephthalic acid intermediate). Many process advantages (including lower pH levels) support the production of this molecule in yeast. Here, we present the first heterologous production of muconic acid in the yeast Saccharomyces cerevisiae. A three-step synthetic, composite pathway comprised of the enzymes dehydroshikimate dehydratase from Podospora anserina, protocatechuic acid decarboxylase from Enterobacter cloacae, and catechol 1,2-dioxygenase from Candida albicans was imported into yeast. Further genetic modifications guided by metabolic modeling and feedback inhibition mitigation were introduced to increase precursor availability. Specifically, the knockout of ARO3 and overexpression of a feedback-resistant mutant of aro4 reduced feedback inhibition in the shikimate pathway, and the zwf1 deletion and over-expression of TKL1 increased flux of necessary precursors into the pathway. Further balancing of the heterologous enzyme levels led to a final titer of nearly 141mg/L muconic acid in a shake-flask culture, a value nearly 24 fold higher than the initial strain. Moreover, this strain has the highest titer and second highest yield of any reported shikimate and aromatic amino acid-based molecule in yeast in a simple batch condition. This work collectively demonstrates that yeast has the potential to be a platform for the bioproduction of muconic acid and suggests an area that is ripe for future metabolic engineering efforts.
    Metabolic Engineering 11/2012; · 6.86 Impact Factor
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    ABSTRACT: Highlights ► Demand for speed of development and low cost drive the need for cell line development technologies. ► Advancements in genome targeting enable precise and robust transgene expression and deletions. ► cis-Acting and trans-acting elements enable control of gene expression and complex circuit design. ► These technologies enable more complex metabolic and pathway engineering of mammalian systems. ► Advancements in these areas will drive advances in cell line development.
    Current Opinion in Chemical Engineering. 11/2012; 1(4):403–410.
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    ABSTRACT: Many metabolic engineering and genetic engineering applications in yeast rely on the use of plasmids. Despite their pervasive use and the diverse collections available, there is a fundamental lack of understanding of how commonly used DNA plasmids affect the cell's ability to grow and how the choice of plasmid components can influence plasmid load and burden. In this study, we characterized the major attributes of the 2μ and centromeric plasmids typically used in yeast by examining the impact of choice of selection marker, promoter, origin of replication, and strain ploidy on conferred growth rates and plasmid copy number. We conclude that the "plasmid burden," as demonstrated by a reduced growth rate, is primarily due to the choice of selection marker, especially when auxotrophic markers are utilized. The plasmid burden traditionally attributed to replication and maintenance of plasmid DNA plays only a minor role in haploid yeast yet is much more significant in diploid strains. The selection marker can also significantly change plasmid copy number. In fact, plasmid copy number can be influenced to some extent by all of the parameters tested. The information presented in this study will allow for more rational design and selection of plasmids for engineering applications. © 2012 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.
    FEMS Yeast Research 10/2012; · 2.44 Impact Factor
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    ABSTRACT: Both varied and strong promoters are essential for metabolic and pathway engineering applications in any host organism. To enable this capacity, here we demonstrate a generalizable method for the de novo construction of strong, synthetic hybrid promoter libraries. Specifically, we demonstrate how promoter truncation and fragment dissection analysis can be utilized to identify both novel upstream activating sequences (UAS) and core promoters-the two components required to generate hybrid promoters. As a base case, the native TEF promoter in Yarrowia lipolytica was examined to identify putative UAS elements that serve as modular synthetic transcriptional activators. Resulting synthetic promoters containing a core promoter region activated by between one and twelve tandem repeats of the newly isolated, 230 nucleotide UAS(TEF)#2 element showed promoter strengths 3- to 4.5-fold times the native TEF promoter. Further analysis through transcription factor binding site abrogation revealed the GCR1p binding site to be necessary for complete UAS(TEF)#2 function. These various promoters were tested for function in a variety of carbon sources. Finally, by combining disparate UAS elements (in this case, UAS(TEF) and UAS1B), we developed a high-strength promoter with for Y. lipolytica with an expression level of nearly sevenfold higher than that of the strong, constitutive TEF promoter. Thus, the general strategy described here enables the efficient, de novo construction of synthetic promoters to both increase native expression capacity and to produce libraries for tunable gene expression.
    Applied Microbiology and Biotechnology 09/2012; · 3.81 Impact Factor
  • John Blazeck, Hal S Alper
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    ABSTRACT: Synthetic control of gene expression is critical for metabolic engineering efforts. Specifically, precise control of key pathway enzymes (heterologous or native) can help maximize product formation. The fundamental level of transcriptional control takes place at promoter elements that drive gene expression. Endogenous promoters are limited in that they do not fully sample the complete continuum of transcriptional control, and do not maximize the transcription levels achievable within an organism. To address this issue, several attempts at promoter engineering have shown great promise both in expanding the cell-wide transcriptional capacity of an organism and in enabling tunable levels of gene expression. Thus, this review highlights the recent advances and approaches for altering gene expression control at the promoter level. Furthermore, we propose that recent advances in the understanding of transcription factors and their DNA-binding sites will enable rational and predictive control of gene expression.
    Biotechnology Journal 08/2012; · 3.71 Impact Factor
  • Hal Alper, Wilfried Weber
    Current Opinion in Biotechnology 07/2012; 23(5):641-3. · 8.04 Impact Factor
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    Sun-Mi Lee, Taylor Jellison, Hal S Alper
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    ABSTRACT: The heterologous expression of a highly functional xylose isomerase pathway in Saccharomyces cerevisiae would have significant advantages for ethanol yield, since the pathway bypasses cofactor requirements found in the traditionally used oxidoreductase pathways. However, nearly all reported xylose isomerase-based pathways in S. cerevisiae suffer from poor ethanol productivity, low xylose consumption rates, and poor cell growth compared with an oxidoreductase pathway and, additionally, often require adaptive strain evolution. Here, we report on the directed evolution of the Piromyces sp. xylose isomerase (encoded by xylA) for use in yeast. After three rounds of mutagenesis and growth-based screening, we isolated a variant containing six mutations (E15D, E114G, E129D, T142S, A177T, and V433I) that exhibited a 77% increase in enzymatic activity. When expressed in a minimally engineered yeast host containing a gre3 knockout and tal1 and XKS1 overexpression, the strain expressing this mutant enzyme improved its aerobic growth rate by 61-fold and both ethanol production and xylose consumption rates by nearly 8-fold. Moreover, the mutant enzyme enabled ethanol production by these yeasts under oxygen-limited fermentation conditions, unlike the wild-type enzyme. Under microaerobic conditions, the ethanol production rates of the strain expressing the mutant xylose isomerase were considerably higher than previously reported values for yeast harboring a xylose isomerase pathway and were also comparable to those of the strains harboring an oxidoreductase pathway. Consequently, this study shows the potential to evolve a xylose isomerase pathway for more efficient xylose utilization.
    Applied and Environmental Microbiology 06/2012; 78(16):5708-16. · 3.95 Impact Factor
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    ABSTRACT: A dynamic range of well-controlled constitutive and tunable promoters are essential for metabolic engineering and synthetic biology applications in all host organisms. Here, we apply a synthetic hybrid promoter approach for the creation of strong promoter libraries in the model yeast, Saccharomyces cerevisiae. Synthetic hybrid promoters are composed of two modular components-the enhancer element, consisting of tandem repeats or combinations of upstream activation sequences (UAS), and the core promoter element. We demonstrate the utility of this approach with three main case studies. First, we establish a dynamic range of constitutive promoters and in doing so expand transcriptional capacity of the strongest constitutive yeast promoter, P(GPD) , by 2.5-fold in terms of mRNA levels. Second, we demonstrate the capacity to impart synthetic regulation through a hybrid promoter approach by adding galactose activation and removing glucose repression. Third, we establish a collection of galactose-inducible hybrid promoters that span a nearly 50-fold dynamic range of galactose-induced expression levels and increase the transcriptional capacity of the Gal1 promoter by 15%. These results demonstrate that promoters in S. cerevisiae, and potentially all yeast, are enhancer limited and a synthetic hybrid promoter approach can expand, enhance, and control promoter activity. Biotechnol. Bioeng. 2012; 109: 2884-2895. © 2012 Wiley Periodicals, Inc.
    Biotechnology and Bioengineering 05/2012; 109(11):2884-95. · 4.16 Impact Factor
  • Kathleen A Curran, Hal S Alper
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    ABSTRACT: The field of Metabolic Engineering has recently undergone a transformation that has led to a rapid expansion of the chemical palate of cells. Now, it is conceivable to produce nearly any organic molecule of interest using a cellular host. Significant advances have been made in the production of biofuels, biopolymers and precursors, pharmaceuticals and nutraceuticals, and commodity and specialty chemicals. Much of this rapid expansion in the field has been, in part, due to synergies and advances in the area of systems biology. Specifically, the availability of functional genomics, metabolomics and transcriptomics data has resulted in the potential to produce a wealth of new products, both natural and non-natural, in cellular factories. The sheer amount and diversity of this data however, means that uncovering and unlocking novel chemistries and insights is a non-obvious exercise. To address this issue, a number of computational tools and experimental approaches have been developed to help expedite the design process to create new cellular factories. This review will highlight many of the systems biology enabling technologies that have reduced the design cycle for engineered hosts, highlight major advances in the expanded diversity of products that can be synthesized, and conclude with future prospects in the field of metabolic engineering.
    Metabolic Engineering 05/2012; 14(4):289-97. · 6.86 Impact Factor
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    ABSTRACT: Establishing causative links between protein functional domains and global gene regulation is critical for advancements in genetics, biotechnology, disease treatment, and systems biology. This task is challenging for multifunctional proteins when relying on traditional approaches such as gene deletions since they remove all domains simultaneously. Here, we describe a novel approach to extract quantitative, causative links by modulating the expression of a dominant mutant allele to create a function-specific competitive inhibition. Using the yeast histone acetyltransferase Gcn5p as a case study, we demonstrate the utility of this approach and (1) find evidence that Gcn5p is more involved in cell-wide gene repression, instead of the accepted gene activation associated with HATs, (2) identify previously unknown gene targets and interactions for Gcn5p-based acetylation, (3) quantify the strength of some Gcn5p-DNA associations, (4) demonstrate that this approach can be used to correctly identify canonical chromatin modifications, (5) establish the role of acetyltransferase activity on synthetic lethal interactions, and (6) identify new functional classes of genes regulated by Gcn5p acetyltransferase activity--all six of these major conclusions were unattainable by using standard gene knockout studies alone. We recommend that a graded dominant mutant approach be utilized in conjunction with a traditional knockout to study multifunctional proteins and generate higher-resolution data that more accurately probes protein domain function and influence.
    PLoS ONE 04/2012; 7(4):e36193. · 3.53 Impact Factor
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    ABSTRACT: Cre recombinase is a commonly-used genome editing tool suitable for site-specific integrations in mammalian genomes; however, the efficiency of transgenic swapping events compared to excision remains limited. Here we sought to identify important parameters and limiting factors that influence swapping propensity in this system, especially when using one wild-type loxP site. To modulate and increase the occurrence of swapping events, we identified two novel parameters. First, we identified the loxFAS-loxP pairing, a sequence never before used in mammalian systems, as the best choice for increasing swapping events in human cell lines. Second, for the first time we implicate the importance of delayed introduction of Cre DNA for optimal swapping efficiency. This same modification could potentially be of use to other systems catalyzing trimolecular reactions such as ΦC31 integrase and FLP recombinase where we hypothesize that transport of the exchange cassette is likewise initially rate limiting. The total number of recombination events, but not the ratio of swapping to excision, was found to be influenced by the quantity of Cre DNA transfected. Through this study, we were able to obtain Cre-mediated swapping frequencies of 8-12% without antibiotic enrichment, which represents nearly an order of magnitude increase over prior reports in the literature.
    Biotechnology Journal 04/2012; 7(7):898-908. · 3.71 Impact Factor
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    ABSTRACT: Traditional metabolic pathway engineering rarely considers the influence of molecular transport. Here, we describe the directed evolution of two heterologous transporters, Candida intermedia GXS1 and Scheffersomyces stipitis XUT3. Growth rate on xylose was improved up to 70% by mutant transporter expression. Most mutants were found to exhibit vastly improved V(max) values and display an increase in high cell density sugar consumption rates. Mixed glucose and xylose fermentations reveal that mutant transporters can alter the diauxic shift dynamics and the simultaneous sugar utilization capacity of the host strain. Analysis of mutations highlights several important residues influencing transporter function including point mutations at F40 of C. intermedia GXS1 and at E538 of S. stipitis XUT3. This work is the first to demonstrate that molecular transporter proteins can be improved for biotechnological applications through directed evolution in yeast.
    Metabolic Engineering 03/2012; 14(4):401-11. · 6.86 Impact Factor
  • Ben Reed, John Blazeck, Hal Alper
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    ABSTRACT: Synthetic alkane-inducible biosensors have applications as detectors for environmental hydrocarbon contamination and as novel inducible expression systems with low-cost inducers. Here, we have assembled and evolved an alkane-responsive biosensor with a fluorescence output signal in Escherichia coli by utilizing regulatory machinery from Pseudomonas putida's alkane metabolism. Within our system, the transcriptional regulator, AlkSp, is activated by the presence of alkanes and binds to the P(alkB) promoter, stimulating transcription of a Green Fluorescent Protein reporter. Through two successive rounds of directed evolution via error prone PCR and fluorescence activated cell sorting, we isolated alkS mutants enabling up to a 5 fold increase in fluorescence output signal in response to short-chain alkanes such as hexane and pentane. Further characterization of selected mutants demonstrated altered responsiveness to a wide range of linear alkanes (pentane to dodecane). Sequence analysis highlighted the S470T mutation as a likely candidate responsible for increased effectiveness of the AlkS protein for short-chain alkanes. This work represents the first evolution of a synthetic biosensor system for alkanes.
    Journal of Biotechnology 02/2012; 158(3):75-9. · 3.18 Impact Factor
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    ABSTRACT: The promises of modern biotechnology hinge upon the hope that we can understand microscopic cellular complexity and in doing so create novel function. In this regard, the fields of systems and synthetic biology are important for accelerating both our understanding of biological systems and our ability to quantitatively engineer cells. At the nexus of these two fields is a unique synergy that can help attain these goals. Thus, the next greatest advances in biology and biotechnology are arising at the intersection of the top-down systems approach and the bottom-up synthetic approach. Collectively, these developments enable the precise control of cellular state for systems studies and the discovery of novel parts, control strategies, and interactions for the design of robust synthetic function. This review seeks to highlight this activity as well as provide a perspective for future directions. Combining these efforts can provide novel insights into cellular function and lead to robust, novel synthetic design.
    Current Opinion in Biotechnology 01/2012; 23(5):712-7. · 8.04 Impact Factor
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    ABSTRACT: Metabolic engineers modify biological systems through the use of modern molecular biology tools in order to obtain desired phenotypes. However, due to the extreme complexity and interconnectedness of metabolism in all organisms, it is often difficult to a priori predict which changes will yield the optimal results. Flux balance analysis (FBA) is a mathematical approach that uses a genomic-scale metabolic network models to afford in silico prediction and optimization of metabolic changes. In particular, a genome-scale approach can help select gene targets for knockout and overexpression. This approach can be used to help expedite the strain engineering process. Here, we give an introduction to the use of FBA and provide details for its implementation in a microbial metabolic engineering context.
    Methods in molecular biology (Clifton, N.J.) 01/2012; 834:197-216. · 1.29 Impact Factor
  • Source
    Hal S Alper
    Computational and structural biotechnology journal. 01/2012; 3:e201210001.
  • Amanda M Lanza, Hal S Alper
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    ABSTRACT: Cellular hosts are widely used for the production of chemical compounds, including pharmaceutics, fuels, and specialty chemicals. However, common metabolic engineering techniques are limited in their capacity to elicit multigenic, complex phenotypes. These phenotypes can include non-pathway-based traits, such as tolerance and productivity. Global transcription machinery engineering (gTME) is a generic methodology for eliciting these complex cellular phenotypes. In gTME, dominant mutant alleles of a transcription-related protein are screened for their ability to reprogram cellular metabolism and regulation, resulting in a unique and desired phenotype. gTME has been successfully applied to both prokaryotic and eukaryotic systems, resulting in improved environmental tolerances, metabolite production, and substrate utilization. The underlying principle involves creating mutant libraries of transcription factors, screening for a desired phenotype, and iterating the process in a directed evolution fashion. The successes of this approach and details for its implementation and application are described here.
    Methods in molecular biology (Clifton, N.J.) 01/2012; 813:229-48. · 1.29 Impact Factor

Publication Stats

2k Citations
406.72 Total Impact Points


  • 2009–2014
    • University of Texas at Austin
      • Department of Chemical Engineering
      Austin, Texas, United States
    • Whitehead Institute for Biomedical Research
      Cambridge, Massachusetts, United States
  • 2012
    • Korea Institute of Science and Technology
      Sŏul, Seoul, South Korea
  • 2005–2009
    • Massachusetts Institute of Technology
      • Department of Chemical Engineering
      Cambridge, MA, United States
  • 2006
    • Technische Universität Berlin
      Berlín, Berlin, Germany