The Dictyostelium discoideum RACK1 orthologue has roles in growth and development

Background: The receptor for activated C-kinase 1 (RACK1) is a
conserved protein belonging to the WD40 repeat family of proteins.
It folds into a beta propeller with seven blades which allow
interactions with many proteins. Thus it can serve as a scaffolding
protein and have roles in several cellular processes. Results: We
identified the product of the Dictyostelium discoideum gpbB gene as
the Dictyostelium RACK1 homolog. The protein is mainly cytosolic
but can also associate with cellular membranes. DdRACK1 binds to
phosphoinositides (PIPs) in protein-lipid overlay and
liposome-binding assays. The basis of this activity resides in a
basic region located in the extended loop between blades 6 and 7 as
revealed by mutational analysis. Similar to RACK1 proteins from
other organisms DdRACK1 interacts with G protein subunits alpha,
beta and gamma as shown by yeast two-hybrid, pull-down, and
immunoprecipitation assays. Unlike the Saccharomyces cerevisiae and
Cryptococcus neoformans RACK1 proteins it does not appear to take
over G beta function in D. discoideum as developmental and other
defects were not rescued in G beta null mutants overexpressing
GFP-DdRACK1. Overexpression of GFP-tagged DdRACK1 and a mutant
version (DdRACK1mut) which carried a charge-reversal mutation in
the basic region in wild type cells led to changes during growth
and development. Conclusion: DdRACK1 interacts with heterotrimeric
G proteins and can through these interactions impact on processes
specifically regulated by these proteins.