Abstract
The villin/gelsolin/fragmin superfamily is a major group of Ca2+-dependent actin-binding proteins (ABPs) involved in various cellular processes. Members of this superfamily typically possess three or six tandem gelsolin-like (G) domains, and each domain plays a distinct role in actin filament dynamics. Although the activities of most G domains have been characterized, the biochemical function of the G3 domain remains poorly understood. In this study, we carefully compared the detailed biochemical activities of ABP29 (a new member of this family that contains the G1-G2 domains of lily ABP135) and ABP135G1-G3 (which contains the G1-G3 domains of lily ABP135). In the presence of high Ca2+ levels in vitro (200 and 10 μM), ABP135G1-G3 exhibited greater actin severing and/or depolymerization and nucleating activities than ABP29, and these proteins had similar actin capping activities. However, in the presence of low levels of Ca2+ (41 nM), ABP135G1-G3 had a weaker capping activity than ABP29. In addition, ABP29 inhibited F-actin depolymerization, as shown by dilution-mediated depolymerization assay, differing from the typical superfamily proteins. In contrast, ABP135G1-G3 accelerated F-actin depolymerization. All of these results demonstrate that the G3 domain plays specific roles in regulating the activities of the lily villin/gelsolin/fragmin superfamily proteins.
Highlights
The villin/gelsolin/fragmin superfamily is an important class of multifunctional actin-binding proteins (ABPs) that regulate dynamic remodeling of the actin cytoskeleton via actin nucleating, severing, capping and bundling activities in eukaryotes [1,2,3]
To identify whether the G3 domain has an effect on the activities of villin/gelsolin/fragmin superfamily members, we generated different truncated variants of lily ABP135 and ABP29 using deletion mutagenesis (Fig 1A)
Actin cytoskeleton dynamics are fundamental to the role of the cytoskeleton in pollen tube growth, which is directly regulated by numerous ABPs [18,51]
Summary
The villin/gelsolin/fragmin superfamily is an important class of multifunctional actin-binding proteins (ABPs) that regulate dynamic remodeling of the actin cytoskeleton via actin nucleating, severing, capping and bundling activities in eukaryotes [1,2,3]. These superfamily proteins are typified by the possession of three or six G domains [1,4,5]. The smallest identified member of the superfamily is ABP29 [20], which contains only the G1 and G2 domains and part of the G2-G3 linker from Lilium pollen and is an alternative splicing product of plant ABP135 [20,21]
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