Heimdallarchaea encodes profilin with eukaryotic-like actin regulation and polyproline binding

Area of Science:

• Cell biology
• Archaea
• Eukaryogenesis

Background:

• The origin of eukaryotic cells involves a symbiosis between an archaeal host and an alphaproteobacterium.
• Profilins regulate actin polymerization, a key process in eukaryotic cells.
• Previous studies on Asgard archaeal profilins suggested polyproline interactions evolved later in eukaryotes.

Purpose of the Study:

• To investigate the function and evolutionary origin of profilin from Heimdallarchaeota LC3, an Asgard archaeon.
• To determine if Heimdallarchaeota profilin interacts with phospholipids and polyproline motifs.

Main Methods:

• 3D structure determination of Heimdallarchaeota LC3 profilin.
• In vitro assays to test inhibition of eukaryotic and archaeal actin polymerization.
• Analysis of interactions with phospholipids (PIP2) and polyproline repeats.

Main Results:

• Heimdallarchaeota profilin (heimProfilin) inhibits eukaryotic actin polymerization.
• heimProfilin binds to phospholipids (PIP2).
• heimProfilin interacts with polyproline motifs, unlike previously studied Asgard profilins.
• heimProfilin also inhibits actin polymerization from Heimdallarchaeota.

Conclusions:

• The findings suggest that interactions with polyproline motifs predate the emergence of eukaryotes.
• A complex cytoskeleton may have existed in the last common ancestor of eukaryotes.
• This challenges the notion that key profilin-actin regulatory mechanisms evolved solely within the eukaryotic lineage.