N-terminal acetylation and arginylation of actin determines the architecture and assembly rate of linear and branched actin networks.

The great diversity in actin network architectures and dynamics is exploited by cells to drive fundamental biological processes, including cell migration, endocytosis and cell division. While it is known that this versatility is the result of the many actin-remodeling activities of actin-binding proteins, such as Arp2/3 and Cofilin, recent work also implicates post-translational acetylation or arginylation of the actin N-terminus itself as an equally important regulatory mechanism. However, the molecular mechanisms by which acetylation and arginylation alter the properties of actin are not well understood. Here, we directly compare how processing and modification of the N-terminus of actin affects its intrinsic polymerization dynamics and its remodeling by actin-binding proteins that are essential for cell migration. We find that in comparison to acetylated actin, arginylated actin reduces intrinsic as well as formin-mediated elongation and Arp2/3-mediated nucleation. By contrast, there are no significant differences in Cofilin-mediated severing. Taken together, these results suggest that cells can employ these differently modified actins to regulate actin dynamics. In addition, unprocessed actin with an N-terminal methionine residue shows very different effects on formin-mediated-elongation, Arp2/3-mediated nucleation, and severing by Cofilin. Altogether, this study shows that the nature of the N-terminus of actin can promote distinct actin network dynamics, which can be differentially used by cells to locally finetune actin dynamics at distinct cellular locations, such as at the leading edge.