Relatives discovered: Membrane proteins of cyanobacteria and higher organisms are structurally highly similar

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The cells of life forms possess proteins which modify and shape cellular membranes, performing significant functions. Although the cell membrane encloses the cell interior, it undergoes frequent alterations, such as invagination, membrane budding or fusion processes, which also require several proteins. These proteins were earlier believed to be present mainly or only in advanced organisms. But in the last two decades, research has identified or predicted the presence of these proteins in simple organisms that lack nuclei. In a collaborative study, a protein that remodels membranes in cyanobacteria has been documented for the first time. It was suspected that such a bacterial protein exists, but confirmation was still pending. The protein studied is presumably a bacterial equivalent of the protein found in higher organisms, such as animals and plants.

Membrane proteins also discovered in prokaryotes

Proteins present in membranes aid in multiple membrane remodeling and mending processes to maintain cell viability in the face of membrane damage. Over the last ten years, these proteins have also been detected in prokaryotes, which are basic organisms that lack a cellular nucleus. Numerous among them exhibit resemblances to proteins that were believed to exist exclusively in more complicated eukaryotic organisms like animals and plants, which possess a cellular nucleus.

Proteins known as dynamins and dynamin-like proteins were initially assumed to be exclusive to eukaryotes until a bioinformatics study in 1999 suggested the presence of bacterial dynamin-like proteins or DLPs. These DLPs are part of the dynamin protein superfamily and play a role in several membrane remodeling processes in eukaryotes.

Researchers from Johannes Gutenberg University Mainz (JGU) and Forschungszentrum Jülich, along with participation from Heinrich Heine University Düsseldorf (HHU), have discovered a specific DLP called SynDLP in a cyanobacterium's genome. "We previously thought that we would only find this type of protein in eukaryotic cells," said Professor Dirk Schneider, head of the Membrane Proteins group at JGU. "SynDLP has structural characteristics that were assumed to exist solely in higher organisms," added Professor Carsten Sachse, a scientist at Forschungszentrum Jülich and HHU professor. "The structural properties of SynDLP imply that it is the nearest recognized bacterial ancestor of eukaryotic dynamin," Sachse explained the findings. "We speculate that this protein was already present in a primitive cell before it developed further into cells with and without a nucleus," Schneider concluded.

Cyanobacteria use an internal membrane system for photosynthesis

Cyanobacteria, also known as blue-green bacteria, are some of the oldest living organisms on our planet. They are named so because of their distinct color. In contrast to other bacteria, they have a secondary internal membrane system, which is responsible for the light reactions of photosynthesis. However, the membrane is vulnerable to damage due to the light reaction and requires constant repair and remodeling. Thus, proteins involved in membrane remodeling are especially crucial for reconstructing or repairing the membrane.

"We are currently uncertain of SynDLP's role in membrane dynamics," explained Professor Dirk Schneider. It seems to be non-essential under laboratory conditions. "However, it wouldn't have been preserved for billions of years if it weren't crucial," suggested the chemist from Mainz University. Moving forward, the researchers plan to explore this topic further and examine precisely what function the protein serves in bacterial cells.

Long-term research cooperation bears fruit

The eight-year research project, which has just been published in Nature Communications, was spearheaded by three young scientists: Dr. Ruven Jilly and Lucas Gewehr from JGU and Dr. Benedikt Junglas from Forschungszentrum Jülich, formerly a doctoral student at the Max Planck Graduate Center with Johannes Gutenberg University Mainz (MPGC). The project also involved collaborators from the Max Planck Institute for Polymer Research in Mainz and Aarhus University in Denmark.

Publications:
L. Gewehr et al., SynDLP is a dynamin-like protein of Synechocystis sp. PCC 6803 with eukaryotic features, Nature Communications 14: 2156, 14 April 2023,
DOI: 10.1038/s41467-023-37746-9
https://www.nature.com/articles/s41467-023-37746-9

C. Siebenaller, D. Schneider, Cyanobacterial membrane dynamics in the light of eukaryotic principles, Bioscience Reports 43: 2, 23 February 2023, 
DOI: 10.1042/BSR20221269
https://portlandpress.com/bioscirep/article/43/2/BSR20221269/232406/Cyanobacterial-membrane-dynamics-in-the-light-of