Abstract
Actin belongs to the most abundant proteins in eukaryotic cells which harbor usually many conventional actin isoforms as well as actin-related proteins (Arps). To get an overview over the sometimes confusing multitude of actins and Arps, we analyzed the Dictyostelium discoideum actinome in detail and compared it with the genomes from other model organisms. The D. discoideum actinome comprises 41 actins and actin-related proteins. The genome contains 17 actin genes which most likely arose from consecutive gene duplications, are all active, in some cases developmentally regulated and coding for identical proteins (Act8-group). According to published data, the actin fraction in a D. discoideum cell consists of more than 95% of these Act8-type proteins. The other 16 actin isoforms contain a conventional actin motif profile as well but differ in their protein sequences. Seven actin genes are potential pseudogenes. A homology search of the human genome using the most typical D. discoideum actin (Act8) as query sequence finds the major actin isoforms such as cytoplasmic beta-actin as best hit. This suggests that the Act8-group represents a nearly perfect actin throughout evolution. Interestingly, limited data from D. fasciculatum, a more ancient member among the social amoebae, show different relationships between conventional actins. The Act8-type isoform is most conserved throughout evolution. Modeling of the putative structures suggests that the majority of the actin-related proteins is functionally unrelated to canonical actin. The data suggest that the other actin variants are not necessary for the cytoskeleton itself but rather regulators of its dynamical features or subunits in larger protein complexes.
Highlights
Actin is an abundant and highly conserved globular protein (Gactin) that forms by polymerization into actin filaments (F-actin) a three-dimensional network, the general principle of the actin cytoskeleton in all non-muscle cells [1,2,3]
Whereas Saccharomyces cerevisiae harbors only one gene that codes for a conventional actin, mouse contains 35, and the plant Arabidopsis thaliana 10 actin genes [4,5]
The members of the D. discoideum actinome were identified according to their ‘actin sequence profile’
Summary
Actin is an abundant and highly conserved globular protein (Gactin) that forms by polymerization into actin filaments (F-actin) a three-dimensional network, the general principle of the actin cytoskeleton in all non-muscle cells [1,2,3]. In higher organisms actin isoforms are classified based on cell type and location, their isoelectric points and their amino acid sequences. Due to the relatively large number of actin genes, the D. discoideum genome provides a very good basis to study the ‘actinome’ for potential cellular targets and conserved sequence motifs.
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