Cryo-EM Structure of Actin Filaments from Zea mays Pollen

Actins are among the most abundant and conserved proteins
in eukaryotic cells, where they form filamentous structures that
perform vital roles in key cellular processes. Although large amounts of
data on the biochemical activities, dynamic behaviors, and important
cellular functions of plant actin filaments have accumulated,
their structural basis is elusive. Here, we report a 3.9 Å
structure of the plant actin filament (ZMPA) from Zea mays pollen using
cryo-electron microscopy. The structure shows a right-handed,
double-stranded (two strands running parallel to each other) and staggered
architecture that is stabilized by intra- and interstrand interactions.
While the overall structure resembles that of other actin filaments, its
DNase I-binding loop (D-loop) bends further outward, adopting an open
conformation similar to that of the jasplakinolide- or Beryllium fluoride
(BeFx)-stabilized rabbit skeleton muscle actin (RSMA) filament.
Single-molecule magnetic tweezer analysis revealed that the ZMPA
filament can resist a greater stretching force than the RSMA filament.
Overall, these data provide evidence that plant actin filaments have
greater stability than animal actin filaments, which is important for
their roles as tracks for long-distance vesicle and organelle
transportation.