Skip to main content
SearchLoginLogin or Signup

Polyester synthase for novel bioplastics with tunable properties

Published onDec 01, 2023
Polyester synthase for novel bioplastics with tunable properties
·

This problem statement is a community effort, and we invite comments, criticisms, and suggested edits.

Origin: This problem statement originates from a workshop held by Homeworld Collective on Oct 10, 2023, where speakers presented ideas for how protein engineering could be applied for climate and sustainability. It is based on ideas presented by Nils Averesch, Research Engineer and Group Leader in Civil and Environmental Engineering at Stanford University and NASA's Center for the Utilization of Biological Engineering in Space.

Contributors: Nils Averesch, Paul Reginato, Ariana Caiati

Lead contact: Nils Averesch ([email protected])

General contact: Paul Reginato ([email protected])

Context

Polymer production for manufacturing of plastic materials accounts for ~6% of global fossil fuel use (Beckham, 2021a) and over 100 Mt CO2e/yr of GHG emissions in the US (Beckham, 2021b). Emissions could be avoided by synthesizing polymers in a one-step biological process from sustainable feedstocks. However, currently-produced bioplastics, like polyhydroxybutyrate (PHB) and polylactate (PLA), lack the material properties (tensile strength and stiffness, thermal stability, gas-barrier) to replace most fossil-derived plastics. A wider application spectrum of bioplastics would be a substantial step toward mitigating the emissions of synthetic polymer production by replacing fossil-derived plastics with biopolyesters.

Significance

Via whole-cell catalysis, microbes can directly utilize single-carbon (C1) compounds, derived from CO2 and sustainable energy, for the formation of various monomers and their polymerization into novel biopolyesters (Rosenboom, 2022). These polyesters are biodegradable as well as recyclable through deconstruction (Kratish, 2021). Further, it is possible to expand the utility of biopolyester in place of non-recyclable polymers by tuning their material properties via incorporation of alternative monomers (Ishii-Hyakutake, 2018). Aromatic monomers are of particular interest, especially those with structural analogy to arylates (such as liquid-crystal polymers), which could enable the production of aromatic polyhydroxyalkanoates with previously unreached properties (Averesch, 2023).

In practice, however, tunability of thermal and mechanical properties of biopolyesters is limited by the monomer incorporation efficiency of polyhydroxyalkanoate (PHA) synthase. Improving incorporation efficiency of diverse monomers by PHA synthase would unlock biocatalysis of biopolyesters with tunable material properties.

Goals

Polyester synthase enzymes should be developed that efficiently incorporate a wider range of aromatic monomers. Monomers of significance include terephthalic and furan-2,5-dicarboxylic acid, for PET and PEF synthesis, respectively; and aromatic hydroxy acids such as coumaric, phloretic, hydroxyphenylacetic, para-hydroxybenzoic, salicylic, and vanillic acid, for synthesis of polyhydroxyalkanoates with structural analogy to arylates (Vannini, 2023, Gabirondo, 2020, Gioia 2016, Prasad, 2001). Engineering efforts may focus on the three main sites that determine activity and specificity of PHA synthases: the active site (3 AAs), substrate pocket (6 AAs), and substrate tunnel (6 AAs) (Chen, 2016, Chek, 2017). A key challenge will be developing assays and analytics to rapidly screen enzymes for incorporation of specific desired monomers.

Additional information

Related problem statements

Open Questions

The significance could be clarified by:

  • Analyses describing the economic feasibility of replacing fossil-derived plastics with bioplastics manufacturing via whole-cell biocatalysis from various C1 feedstocks, and the key cost barriers to doing so.

    • Brandon, 2019 describes current challenges of readying sustainable bioplastics production for the consumer market

    • Rosenboom, 2022 tabulates production cost for various synthetic as well as biological plastics are compiled in Table 1, without emphasis on the feedstock

    • Levett, 2016 performs a techno-economic assessment of polyhydroxybutyrate production (PHB) from methane, but PHB has limited applicability

  • Analysis of which biopolyesters, made from which C1 feedstocks, are likely to have the greatest sustainability impact via fossil-derived plastic replacement

The goals could be made more granular and clear by:

  • Estimation of the necessary incorporation rate of specific aromatic monomers in order to make specific impactful biopolyesters.

    • An example is given in Figure 1 of Prasad, 2001, which shows how the fraction 4-hydroxybenzoic acid monomers (HBA) in an HBA-4-hydroxyphenylacetic acid copolymer affects the thermal properties. While this example is only for one specific co-polymer, the relative fractions in order to achieve an observable change will likely be similar for other co-polymers.

The goals would be enabled by:

  • Development of an easy assay for monomer incorporation to enable screening

Assumptions

  • Manufacturing of bioplastics using whole-cell biocatalysis using C1 feedstocks can be done economically to compete with fossil-derived plastics

  • The required volumes of sustainable C1 feedstock will become available to support a plastics economy. At current plastic production rates, ~ 1 Gt of C1 feedstock would be required. If recycling were to increase from the current ~10% to ~90%, that number could be reduced by an order of magnitude, which makes the required scale of infrastructure for production much more feasible.

Comments
0
comment
No comments here
Why not start the discussion?