D-loop dynamics and near-atomic resolution cryoEM structure of phalloidin bound F-actin

• Published in: Structure (London) 2020-04, Vol.28 (5), p.586-593.e3
• Main Authors: Das, Sanchaita, Ge, Peng, Durer, Zeynep A. Oztug, Grintsevich, Elena E., Zhou, Z. Hong, Reisler, Emil
• Format: Article
• Language: English
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2020.04.004

Detailed molecular information on G-actin assembly into filaments (F-actin), and their structure, dynamics and interactions, is essential for understanding their cellular functions. Previous studies indicate that a flexible DNase I binding loop (D-loop, residues 40–50) plays a major role in actin’s conformational dynamics. Phalloidin, a “gold standard” for 6 actin filaments staining, stabilizes them and affects the D-loop. Using disulfide cross-linking in yeast actin D-loop mutant Q41C/V45C, light scattering measurements, and cryoEM reconstructions we probed the constraints of D-loop dynamics and its contribution to F-actin formation/stability. Our data support a model of residues 41–45 distances which facilitate G- to F-actin transition. We report also a 3.3 Å resolution structure of phalloidin-bound F-actin in the ADP-Pi-like (ADP-BeFx) state. It shows the phalloidin binding site on F-actin and how the relative movement between its two protofilaments is restricted by it. Together, our results provide molecular details of F-actin structure and D-loop dynamics. Actin plays crucial roles in biological systems and its DNase 1 binding loop interacts with several actin binding proteins. Das et al. demonstrate that phalloidin (phalllotoxin) “glues” the two strands of actin filaments through additional contacts between protomers