Gatekeeper protein complexes at the outer boundaries of cells make life possible by regulating the passage of key molecules such as nutrients into and out of the cell.

Scientists in Belgium and the Czech Republic have revealed new structural and functional insights on an ancient, evolutionarily conserved protein complex that makes it possible for cells to wrap their membranous arms around and bring essential biomolecules into the cell—a process called endocytosis. The structure and function of cells with nuclei (eukaryotic cells) depend on endocytosis for the continuous exchange of biomolecules through membranes.

Most eukaryotic organisms, except fungi and animals, have retained the ancient TSET protein complex as an endocytic regulator. Unlike other protein complexes involved in trafficking molecules across membranes, structural insight into the ancient TSET complex has remained sketchy until now.

The current study uses an integrated structural approach to reveal the molecular architecture of the plant TSET complex (TPLATE) and identifies key biological functions for specific subunits as to how the complex assembles and interacts with other components of the plasma membrane. The authors also compared differences in the eight-subunit TPLATE complex in plants and its six-subunit counterpart in a slime mold (Dictyostelium) that feeds on bacteria.

TPLATE
TPLATE Structure [The Flanders Institute of Biotechnology]
These findings are reported in the article, “Molecular architecture of the endocytic TPLATE complex,” recently published in Science Advances. The structural insights of this ancient protein complex advance functional and evolutionary understanding of endocytosis. The study will open doors for the generation of novel and safer herbicides and the modulation of stress responses in plants.

A recent discovery showed that plants heavily rely on the TPLATE complex to exchange materials between internal compartments or organelles. The TPLATE complex is not only present in plants, but also in a wide range of other eukaryotes, which suggests it is conserved during evolution. Most members of this ancient protein family have been intensively studied but because TPLATE is not present in common laboratory model organisms such as mice and yeasts, its existence and function remained under the radar.

One research group from the Czech Republic including Martin Potocký, PhD, and Roman Pleskot, PhD, and five teams of scientists at the Flanders Institute for Biotechnology (VIB, Vlaams Instituut voor Biotechnologie) including the groups of Bert De Rybel, PhD, Geert De Jaeger, PhD, and Daniël Van Damme, PhD, from the Center for Plant Systems Biology, Remy Loris, PhD, from the Center for Structural Biology, and Savvas Savvides, PhD, from the Center for Inflammation Research, collaborated to reveal TPLATE’s molecular architecture.

Their integrated structural approach includes a combination of crosslinking mass spectrometry and computer simulations. These new insights revealed the orientation of this complex with respect to the membrane as well as the delicate relationship between the different domains of its subunits.

These findings are important in understanding how the basic and crucial eukaryotic process of endocytosis works. The newly revealed structure of this complex now allows the comparison with known structures of its close relatives that are present in all eukaryotes including animals and yeasts which in turn allows scientists to visualize the evolution of these trafficking complexes.

The collaborative team performed experiments ranging from lipid-binding studies to structural biology approaches. The novel structural insight was mostly generated based on crosslinking mass spectrometry.

“A major benefit of working at VIB is that it greatly encourages and facilitates access to knowledge and expertise that allows research groups to successfully embark on joint projects that lie far beyond their comfort zone,” said Van Damme.