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Bioplastic spun by enzyme may replace petro-plastic says MIT

By Karen Hardison     Nov 15, 2016 in Science
Boston - Bacterial enzymes produce polymer chains that have the properties of plastic. MIT discovered where nutrients enter and polymers exit making bioengineering of bioplastics — replacing petro-plastics — more feasible.
Bacteria enzymes produce long chains of polymers that have properties like plastics. MIT scientists have discovered the structure of a polymer-producing enzyme, as reported by SciTech Daily. This opens the door to potentially replacing toxic petrochemical plastics with biologically produced plastics. Some companies already synthesize bioplastic polymers for medical packaging. The enzyme polyhydroxyalkanoate (PHA) synthase is found in nearly all bacteria and produces large plastic polymers that are normally stored by the enzyme as food.
Researchers at MIT have determined the structure of a bacterial enzyme that can produce biodegradable plastics, an advance that could help chemical engineers tweak the enzyme to make it even more industrially useful.
These polymer bioplastics are of two kinds and are generated as the result of the nutrients ingested by the bacterial enzyme. One class of nutrients generates a hard plastic similar to synthetic petrochemical plastic, and another class of nutrients generates a soft plastic similar to latex rubber.
The company Yield10 Bioscience/Metabolix has already shown the way in PHA biopolymer technology for "a range of consumer packaging applications," as reported by Globe Newswire. The discovery of the enzyme's structure is not expected to lower the cost of making PHA polymers since the process is "not cost-efficient enough to be economically competitive with low-cost conventional plastics derived from oil," according to Yield10's chief scientific officer and vice president of research, Kristi Snell. It is hoped that the discovery of the enzyme's structure will open the way for the development of new polymer materials and applications, as Snell points out.
Critical to understanding the bacterial enzyme's structure was identifying the location of the entry and exit points for the nutrients the enzyme converts to the two kinds of polymer, the hard bioplastic and the soft latex-like rubber. Once these points were located, both marked by the surrounding presence of conserved amino acids, the avenue for enzyme engineering was opened. "I believe you want to have a good fundamental understanding of enzymes like this before you start engineering them," said Catherine Drennan, MIT professor of chemistry and biology and Howard Hughes Medical Institute Investigator.
The paper "Structure of the Catalytic Domain of the Class I Polyhydroxybutyrate Synthase from Cupriavidus necator" appears in the Journal of Biological Chemistry. Catherine Drennan and JoAnne Stubbe, Novartis Professor of Chemistry Emeritus and professor emeritus of biology, are senior authors of the study. Graduate student Elizabeth Wittenborn is the lead author, and former graduate students Marco Jost and Yifeng Wei are co-authors. Jost and Wei mastered the crystallization process for the enzyme. Crystallization is a critical step for successfully performing X-ray crystallography needed to examine the molecular and atomic structure of the target enzyme.
More about Enzyme, PHA polymer, polyhydroxyalkanoate synthase, Mit
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