Actin filament bundling by the Arabidopsis VILLIN4 C-terminus involves the basic segment of the IDR linker and is sensitive to temperature and ionic strength

Abstract

Plant villins are ubiquitous proteins involved in F-actin regulation in all plant organs. Villins consist of folded core and headpiece domains connected by an intrinsically disordered linker. In plant villins these linkers include up to 200 amino acid residues, which is substantially larger than their vertebrate counterparts (~40 residues). Moreover, the linkers in most types of plant villins exhibit a distinct charge partitioning pattern: a larger basic N-terminus and a smaller acidic C-terminus. The roles of these distinct, sizable and disordered linkers in plant villins are not well understood and are currently under active scrutiny. Here we demonstrate that the basic portion of the linker in Arabidopsis thaliana VILLIN4 (AtVLN4) is capable of actin filament bundling. These interactions are also affected by the presence of the adjacent headpiece domain and are altered by temperature and levels of potassium ions, major abiotic regulators that influence plant growth. Based on these findings, we propose that the F-actin bundling capacity of the basic segment in AtVLN4 is responsive to environmental changes and is a uniform property in closely related villins due to high sequence homology across multiple species.