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Crowding Alters Secondary Structure in F-actin Bundles

The cytoskeletal component actin plays a crucial role in various cellular functions, including cell shape regulation and intracellular transport, by forming filaments and networks. Despite the current understanding of actin's morphological versatility, the impact of crowded environments—specifically how actin filaments organize into bundles and how this organization changes the protein secondary structure—remains under-explored. Here, we used two-dimensional infrared (2D IR) spectroscopy and structure based spectral calculations to map out structural changes of actin filaments under two degrees of crowding and bundling.

  • There is a transition from β-sheet to loop conformations with increased actin bundling.
  • Strongly bundled networks show a more "locked" β-sheet structure, with loops becoming less hydrated.
  • This structural transition underscores the loop's role in defining the network morphology and stability, which is crucial for the actin cytoskeleton's adaptability.
  • This understanding will aid in the design of actin gels that respond to dynamic, fueled changes in depletants, a key IRG goal.