Image 1. Polyester microdroplets assembled after dehydration-rehydration. Credit: Tony Z. Jia

 

Life is composed of biological molecules such as proteins, nucleic acids, lipids, etc., and the exploration of the emergence and evolution of biomolecules has been a primary focus of Origins of Life (OoL) research. However, the prebiotic chemical space on early Earth also consisted of “non-biological” molecules, which either have limited, no, or different roles in modern biology. Alpha hydroxy acids (AHAs) are one group of such molecules; AHAs participate in modern metabolism, are abundant prebiotically, and are chemically similar to amino acids (monomers of proteins and enzymes). AHAs have been shown to polymerise spontaneously into polyesters when subjected to wet-dry cycling, a prebiotically relevant polymer formation process.
 
Recent studies have shown the propensity of these polyesters to assemble into membraneless microdroplets, which can show life-like properties such as compartmentalisation and growth. These properties make exploring “non-biological” polyesters as contributors to the origin of life on Earth worthwhile.
 
Enzymes drive almost all biochemical reactions. Thus, one aspect of OoL research focuses on the origin and evolution of prebiotic catalysis. Owing to the structural similarity of polyesters to peptides (short chains of amino acids) and the different chemical interactions that polyesters demonstrate, an international team consisting of researchers from five different countries, led by ELSI’s Specially Appointed Associate Professor Tony Z. Jia and Research Fellow of the National University of Malaysia Kuhan Chandru, sought to explore whether polyesters could have catalysed/driven reactions that led to life´s origins.
 
Polyester-based catalysis/reaction was first categorised into different types, namely, simple polyesters, hyperbranched polyesters, and polyester microdroplets. The team then explored reactions driven/catalysed by each category of polyester in various fields, including applied research, basic science, and existing OoL literature, in hopes of finding prebiotically relevant examples.
 
For example, the team established a link between biodiesel formation and prebiotic chemistry, where prebiotically relevant reactions also present in biodiesel formation can be catalysed by simple polyesters. Similarly, the team discovered that certain simple polyesters that accelerate the hydrolysis of biodegradable polymers used in medical applications might have also catalysed the hydrolysis of primitive polymers, which could be a prebiotically relevant method to regenerate monomers to be freed up for future synthetic polymerisation reactions; cyclical repeating of such hydrolysis/polymerisation reactions could lead to prebiotic evolution. Finally, autocatalysis, an intensively researched topic by the OoL community, could also be facilitated by simple polyesters used in chemical engineering applications and in the degradation of bioplastics.
 
The globular structure of enzymes gives its catalytic functionality in modern cells. Hyperbranched polyesters (HBPs) also have globular structures, have demonstrated catalytic activity, and are proposed to be possible protoenzymes. Indeed, globular HBPs with catalytic activity have been utilised in industrial applications. Additionally, a previous study demonstrated photocatalysis by metals present inside HBPs (metal-scaffolded HBPs), utilised for environmental remediation, which indicates that it is not out of the realm of possibility that ´metalloprotoenzymes´ like HBP-metal complexes could have catalysed reactions on early Earth.
 
The evolution of prebiotic molecules into efficient biomolecular machines found in modern cells today might have been possible only when such molecules were selectively segregated and concentrated from the dilute prebiotic environment, which also may have simultaneously enhanced reaction rates. Coacervates are prebiotic compartments that might have performed such functions, leading to increased reaction kinetics of prebiotic molecules involved. They have also been shown to encapsulate and enhance the catalytic efficiencies of some metabolic enzymes found in modern cells. Polyesters can also form distinct membraneless compartments like coacervates in the form of microdroplets. Although polyester microdroplets can encapsulate biomolecules like RNA, their reaction-driving/catalytic activities have yet to be fully explored. Thus, the researchers of this study have speculated that since polyester microdroplets and coacervates are both formed as a result of some type of phase separation process, the possibility of prebiotic reactions driven/catalysed by polyester microdroplets is not far-fetched and should be a clear avenue of future exploration.
 
This study highlights the importance and empowers the study of non-biological molecules like polyesters in OoL research, a currently underexplored (but important) topic. “Although the reactions driven/catalysed by polyesters presented in this study so far are evidence-based hypotheses taken from examples in other fields, this study can serve as a credible resource for a relevant starting point for OoL researchers to explore prebiotic catalytic polyesters further,” says study first author Arunava Poddar (Visiting Scholar from Blue Marble Space Institute of Science). Additionally, exploring the role of polyesters in the origins of life opens up an avenue to explore ´life as we don´t know it´ on other extraterrestrial bodies in the universe.
 
The study was an invited article published in a special issue on ´Prebiotic catalysis´ in Accounts of Chemical Research.
 

Image 2. The authors of this paper. Credit: The authors
 

Image 3. Overview of the strategy used in the paper. Credit: Arunava Poddar using Canva; stock image provided by ©ESA, with general permission allowed for use, reproduction, broadcast, and public performance for educational, editorial, or informational purposes, including to illustrate press articles.
 

Journal Accounts of Chemical Research
Title of the paper Reactions Driven by Primitive Non-biological Polyesters
Authors Arunava Poddar1,2, Nirmell Satthiyasilan3, Po-Hsiang Wang4,5, Chen Chen6,7,, Ruiqin Yi8, Kuhan Chandru3,9,*, Tony Z. Jia1,6,*
Affiliations
  1. Blue Marble Space Institute of Science, 600 1st Ave, Floor 1, Seattle, Wasington 98104, United States
  2. Research Centre for Experimental Marine Biology and Biotechnology (PiE-UPV/EHU), University of the Basque Country, Areatza Pasealekua, 48620 Plentzia Bizkaia, Basque Country, Spain.
  3. Space Science Center (ANGKASA), Institute of Climate Change, National University of Malaysia, Bandar Baru Bangi, Selangor 43600, Malaysia
  4. Graduate Institute of Environmental Engineering, National Central University, No. 300, Zhongda Rd., Zhongli District, Taoyuan 32001, Taiwan (Republic of China)
  5. Department of Chemical and Materials Engineering, National Central University, No. 300, Zhongda Rd., Zhongli District, Taoyuan 32001, Taiwan (R.O.C.)
  6. Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1-IE-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
  7. Biofunctional Catalyst Research Team, RIKEN Center for Sustainable Resource Science (CSRS), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
  8. State Key Laboratory of Isotope Geochemistry and Chinese Academy of Sciences Center for Excellence in Deep Earth Science, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
  9. Polymer Research Center (PORCE), Faculty of Science and Technology, National University of Malaysia, Bandar Baru Bangi, Selangor 43600, Malaysia
DOI 10.1021/acs.accounts.4c00167
Online published date 16 July 2024