How laboratory evolution and gut microbiome discoveries converge on solving the plastic crisis

The global accumulation of polyethylene terephthalate waste has driven researchers to explore enzymatic solutions from two distinct sources: rational protein engineering of known bacterial enzymes and discovery mining within complex microbial ecosystems. This comparison examines FAST-PETase, an engineered variant of the bacterial enzyme from Ideonella sakaiensis, and HGMP01, a newly discovered enzyme from the human gastrointestinal microbiome, revealing how different evolutionary pressures shape protein structure and function for plastic degradation.​

FAST-PETase represents the culmination of machine learning-guided protein design, incorporating five strategic mutations that enhance both stability and catalytic efficiency at elevated temperatures. The enzyme achieves a 38-fold increase in activity compared to its parent enzyme at 50°C, with modifications that strengthen hydrogen bonding networks and optimize electrostatic interactions near the active site. In contrast, HGMP01 emerged from bioinformatic screening of the Unified Human Gastrointestinal Genome collection, representing an independently evolved solution adapted to the unique chemical environment of the human digestive tract.​

The structural foundation of both enzymes follows the canonical α/β hydrolase fold, characterized by a central twisted β-sheet surrounded by α-helices. FAST-PETase contains 290 amino acids organized around a conserved Ser160-His237-Asp206 catalytic triad, while HGMP01 comprises 275 amino acids with a molecular weight of 30.18 kDa. The shorter sequence length in HGMP01 reflects its distinct evolutionary trajectory within gut bacteria of the Acutalibacteraceae family, organisms known for fermenting complex plant carbohydrates.​

Temperature preferences distinguish these enzymes significantly. FAST-PETase functions optimally at 50°C, approaching the glass transition temperature of PET where polymer chains become more accessible to enzymatic attack. The five mutations work synergistically to elevate the melting temperature to approximately 63°C, a substantial improvement over the wild-type enzyme. HGMP01 exhibits maximal activity at 40°C, consistent with human body temperature and the conditions within the gastrointestinal tract where this enzyme naturally functions.​

pH preferences reveal adaptation to distinct environments. FAST-PETase performs best at pH 9.0, maintaining activity across the moderate range of 6.0 to 9.0. HGMP01 demonstrates remarkable alkaline tolerance, achieving peak activity at pH 10.0 to 11.0 while retaining function down to neutral pH. This alkaline preference correlates with HGMP01’s predicted isoelectric point of 9.12and overall positive surface charge, contrasting with the dipole distribution observed in the parent enzyme of FAST-PETase.​

The catalytic machinery in both enzymes utilizes the classic serine hydrolase mechanism, proceeding through acylation and deacylation stages. FAST-PETase benefits from the N233K mutation, which paradoxically enhances catalysis not by forming a salt bridge as initially proposed, but by altering the chain folding around Glu204. This conformational change increases the basicity of Asp206 in the catalytic triad, strengthening its interaction with protonated His237 and lowering the activation barrier by approximately 4.4 kcal/mol. The specific catalytic residues in HGMP01 remain less characterized, though the enzyme clearly possesses the conserved catalytic triad essential for ester bond hydrolysis.​

Binding site organization reflects each enzyme’s substrate preferences. FAST-PETase maintains the characteristic shallow L-shaped cleft spanning approximately 40 Å, divided into subsites that accommodate multiple PET moieties simultaneously. The wobbly Trp185 residue adopts multiple conformations, facilitating substrate entry and product release through π-π interactions with aromatic groups in PET. HGMP01 shows enhanced activity toward PET nanoparticles, suggesting its binding architecture may favor smaller substrate fragments consistent with the fragmented plastic particles encountered in the digestive environment.​

Sequence relationships provide insight into evolutionary origins. FAST-PETase shares 100% sequence identity with its parent IsPETase aside from the five engineered mutations, maintaining the two disulfide bonds characteristic of this enzyme family. HGMP01 exhibits only 20 to 41% sequence similarity to known PETases, indicating independent evolution. Both enzymes contain the DLH domain, a structural signature common to many esterases and lipases.​

The convergent evolution toward plastic degradation activity through divergent pathways highlights fundamental principles of enzyme adaptation. FAST-PETase achieves superior performance through precise mutation of surface residues that stabilize the protein fold and optimize active site geometry for industrial applications. HGMP01 represents nature’s independent solution, potentially shaped by millennia of exposure to polyester-like compounds in the gut environment. Recent metatranscriptome analysis confirms that HGMP01-like genes are actively expressed in over 20% of surveyed human gut samples, suggesting an ongoing role in managing ingested microplastics.​

These parallel developments underscore both the promise and complexity of biocatalytic plastic recycling. While FAST-PETase demonstrates the power of rational design to create robust industrial biocatalysts, HGMP01 reveals that functional plastic-degrading enzymes have emerged spontaneously in unexpected ecological niches, offering new templates for protein engineering and raising important questions about the biological fate of ingested plastics in human populations.