The same team from the Shenzhen Advanced Institute of the Chinese Academy of Sciences explored the mystery of the origin of eukaryotic cell membrane lipids through synthetic biology

On November 24, 2022, the research group of Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, in collaboration with the research group of Professor Zhang Chuanlun of Southern University of Science and Technology, published a title entitled Angewandte Chemie International Edition Biosynthesis of Hybrid Neutral Lipids with Archaeal and Eukaryotic Research paper by Characteristics in Engineered Saccharomyces cerevisiae.

Relying on the major scientific and technological infrastructure of synthetic biology research in Shenzhen (hereinafter referred to as the "big facility" of synthetic biology), the research team used Saccharomyces cerevisiae as the chassis to realize the heterologous synthesis of archaeal polar cell membrane lipids in eukaryotic cells for the first time, and accidentally observed heterozygous neutral lipids (DGGGO-FA) with both eukaryotic and archaeal characteristics
。

The research team further analyzed the synthesis mechanism of this novel compound, and proposed and partially verified the hypothesis that triacylglycerol (TAG) molecules may be synthesized by archaea for energy storage through bioinformation analysis and experimental characterization, which challenged the general understanding of the scientific community
.

The tree of life is divided into three domains: bacteria, eukary, and Archaea
.

In 1977, American microbiologist Carl Woese stumbled upon archaea through 16S/18S rRNA sequence phylogenetic analysis, according to which prokaryotes were divided into two categories: bacteria and archaea, and together with eukaryotes constitute the three-domain system of the origin of life Three-Domain Hypothesis (Three-Domain).

James, 1988 Based on the classification method of ribosome structural similarity and evolutionary simplicity, Lake revealed that eukaryotes are a branch of archaea, suggesting that eukaryotes may be derived from archaea, and proposed the two-domain system tree of life hypothesis
.
Archaea are single-celled prokaryotic microorganisms, without nuclei, without endometrial system, with circular genomes and lack of splicing introns in the body, which are close to bacteria in cell structure and metabolism; But in the central processes of biology such as DNA replication, transcription and translation, it is more closely
related to eukaryotes.
Humans belong to eukaryotes
.
Are archaea siblings of eukaryotes (three-domain hypothesis) or parents (two-domain hypothesis)? This is one of the great problems in the evolution of
life.

Three-domain system

Two-domain system

The development of metagenomic technology has led to the discovery of Asgard archaea, many of whose genomes carry a large number of eukaryotic signatures Proteins, ESP) encodes genes and is evolutionarily the closest prokaryotic
organism to eukaryotic origin.

The discovery of Asgard archaea is thought to favor the two-domain system tree of life hypothesis: about 18-2 billion years ago, the archaeal ancestors of the Asgard lineage first acquired a primitive cytoskeletal system with membrane deformation and the ability to sort and transport nuclear endosomal material, and then developed an "endosymbiosis" with the bacteria of the Alpha Proteobacteria phylum, and gradually evolved into the most important cell line in modern eukaryotes, mitochondria, which became a key step
in the origin of eukaryotes.

However, endosymbiosis also faces many challenges, one of which is an important unsolved mystery is why the membrane lipomolecular backbone of existing eukaryotic cells and archaeal cells has opposite chirality.
The membrane lipids of modern bacteria and eukaryotic cells are mainly composed of glycerol-3-phosphate (G3P) as the skeleton, while archaeal cell membranes use glycerol-1-phosphate (G1P) as the basic parent nuclear structure, a phenomenon known as Lipid Divide
.
This phenomenon is extremely unusual because the organic molecules that make up life on Earth usually have a single chirality, such as L-type amino acids, D-type nucleotides, and so on
.
Based on the endosymbiosis theory, modern eukaryotic cells should be derived from archaeal hosts, but their membrane lipids have the opposite chirality to archaea and are similar
to those of endocytosed bacteria.
There seems to be an irreconcilable contradiction between the membrane lipid demarcation and the two-domain tree of life, which is one of the great mysteries of
eukaryotic origin.
In previous studies, scientists have constructed heterozygous membrane lipid models with both G1P and G3P based on liposomes and bacteria, but have not yet successfully constructed eukaryotic-archaeal heterozygous models to more directly study the origin of
eukaryotic membrane lipids.

Saccharomyces cerevisiae is a model eukaryotic microorganism with detailed genetic biochemical studies and rich synthetic biology tools, which is an ideal host
for studying the evolution of archaea-eukaryotic membrane lipids 。 Relying on the "big facility" of synthetic biology, the authors used modular DNA assembly methods to construct a biosynthetic pathway of polar lipids in archaeal cell membranes on a large scale, and introduced key synthetic genes from different sources such as methanogenic archaea, sulfide archaea, and Asgard archaea in a "plug and play" manner in the yeast chassis, and successfully synthesized polar lipids with archaeal ether bond characteristics (Figure 1).

Based on this model, the authors found that Saccharomyces cerevisiae also has the ability
to synthesize G1P.
At the same time, the authors obtained the first biochemical experimental evidence to support the synthesis of Heterozygous membrane lipids with both G1P and G3P chiral GRGGPS enzymes derived from Asgard archaea (Figure 2).

These observations suggest that the membrane lipid demarcation is not as strict
as originally thought.