Nav: Home

Mystery of biological plastic synthesis machinery unveiled

November 30, 2016

Daejeon, Republic of Korea, Nov. 30, 2016 -- Plastics and other polymers are used every day. These polymers are mostly made from fossil resources through petrochemical refinery process. On the other hand, many microorganisms naturally synthesize polyesters known as polyhydroxyalkanoates (PHAs) as distinct granules inside the cell. PHAs are a family of microbial polyesters that have attracted much attention as biodegradable and biocompatible plastics and elastomers that can substitute petrochemical counterparts. There have been numerous papers and patents on gene cloning and metabolic engineering of PHA biosynthetic machineries, biochemical studies, and production of PHAs; simple Google search with "polyhydroxyalkanoates" returns with 223,000 document pages. PHAs have always been considered an amazing example of biological polymer synthesis. It is astounding to see PHAs of 500 kDa to sometimes as high as 10,000 kDa can be synthesized in vivo by PHA synthase, the key polymerizing enzyme in PHA biosynthesis. Thus, there has been great interest in determining the crystal structure of PHA synthase over the last 30 years, but unfortunately without success. Thus, the characteristics and molecular mechanisms of PHA synthase have so far been under a dark veil.

In two papers published back-to-back in Biotechnology Journal online on November 30, 2016, a Korean research team led by Professor Kyung-Jin Kim at Kyungpook National University and Distinguished Professor Sang Yup Lee at the Korea Advanced Institute of Science and Technology (KAIST) reported the crystal structure of PHA synthase from Ralstonia eutropha, the best studied bacterium for PHA production. The research team also reported the structural basis for the detailed molecular mechanisms of PHA biosynthesis. The crystal structure has been deposited to Protein Data Bank in February 2016. After deciphering the crystal structure of the catalytic domain of PHA synthase in addition to other structural studies on whole enzyme and related proteins, the team performed experiments to elucidate mechanisms of the enzyme reaction, validating detailed structures, enzyme engineering, and N-terminal domain studies among others.

Through several biochemical studies based on crystal structure, authors show that PHA synthase exists as a dimer and is divided into two distinct domains, the N-terminal domain (RePhaC1ND) and the C-terminal domain (RePhaC1CD). The RePhaC1CD catalyzes the polymerization reaction via a non-processive ping-pong mechanism using a Cys-His-Asp catalytic triad. The two catalytic sites of the RePhaC1CD dimer are positioned 33.4 Å apart, suggesting that the polymerization reaction occurs independently at each site. This study also presents the structure-based mechanisms for substrate specificities of various PHA synthases from different classes.

Professor Lee, who has been working on this topic for more than 20 years, said, "The results and information presented in these two papers have been very much awaited not only in the PHA community, but also metabolic engineering, bacteriology/microbiology, and in general biological sciences communities. The structural information on PHA synthase together with reaction mechanisms deciphered will be valuable for understanding the detailed mechanisms of biosynthesizing this important energy/redox storage material, and also for the rational engineering of PHA synthases to produce designer bioplastics from various monomers more efficiently."
-end-
Indeed, these two papers published in Biotechnology Journal finally unveil the 30-year mystery of machinery of biological polyester synthesis and will serve as an essential compass in creating designer and more efficient bioplastic machineries.

Jieun Kim, Yeo-Jin Kim, So Young Choi, Sang Yup Lee and Kyung-Jin Kim. "Crystal structure of Ralstonia eutropha polyhydroxyalkanoate synthase C-terminal domain and reaction mechanisms." Biotechnology Journal. DOI: 10.1002/biot.201600648 http://onlinelibrary.wiley.com/doi/10.1002/biot.201600648/abstract

Yeo-Jin Kim, So Young Choi, Jieun Kim, Kyeong Sik Jin, Sang Yup Lee and Kyung-Jin Kim. "Structure and function of the N-terminal domain of Ralstonia eutropha polyhydroxyalkanoate synthase, and the proposed structure and mechanisms of the whole enzyme." Biotechnology Journal. DOI: 10.1002/biot.201600649 http://onlinelibrary.wiley.com/doi/10.1002/biot.201600649/abstract

The Korea Advanced Institute of Science and Technology (KAIST)

Related Enzyme Articles:

Enzyme catalyzed decomposition of 4-hydroxycyclophosphamide
Oxazaphosphorine cytostatics (Cyclophosphamide, Ifosfamide) are often used and very effective anticancer agents; but so far little is known about the molecular basis for the antitumor effect.
The carpenter enzyme gives DNA the snip
Enzyme follows a two-step verification system before cutting and repairing DNA damage.
Cellular senescence prevented by the SETD8 enzyme
An enzyme that blocks cellular senescence and its mechanisms has been discovered by a Japanese research team.
Enzyme key to learning in fruit flies
University of California, Riverside-led research finds enzyme that is key to learning in fruit flies.
Old enzyme, new role
A team of researchers at the University of Delaware has discovered a new function for an enzyme that has long been known to have a central role in bacterial metabolism.
Enzyme research provides a new picture of depression
Depression is the predominant mental disease and constitutes the most common cause of morbidity in developed countries.
Mysteries of enzyme mechanism revealed
International team led by University of Leicester unveil a hidden step in enzyme mechanism.
Single enzyme controls 2 plant hormones
Scientists at Washington University in St. Louis have isolated the first enzyme shown to be capable of controlling the levels of two distinct plant hormones, involved both in normal growth and in responses to infections.
New enzyme-mapping advance could help drug development
Scientists at MIT and the University of São Paulo in Brazil have identified the structure of an enzyme that could be a good target for drugs combatting three diseases common in the developing world.
Severity of enzyme deficiency central to favism
The congenital disease favism causes sickness and even jaundice in patients after they consume beans.

Related Enzyme Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Setbacks
Failure can feel lonely and final. But can we learn from failure, even reframe it, to feel more like a temporary setback? This hour, TED speakers on changing a crushing defeat into a stepping stone. Guests include entrepreneur Leticia Gasca, psychology professor Alison Ledgerwood, astronomer Phil Plait, former professional athlete Charly Haversat, and UPS training manager Jon Bowers.
Now Playing: Science for the People

#524 The Human Network
What does a network of humans look like and how does it work? How does information spread? How do decisions and opinions spread? What gets distorted as it moves through the network and why? This week we dig into the ins and outs of human networks with Matthew Jackson, Professor of Economics at Stanford University and author of the book "The Human Network: How Your Social Position Determines Your Power, Beliefs, and Behaviours".