G-type immunoglobulins (IgGs) are extensively used in the pharmaceutical industry against various diseases, being also crucial in multiple immunoassays. The production of secondary monoclonal antibodies (Abs) for IgG detection is not cost-effective, while polyclonal antibody production still depends on laboratory animals, which raises concerns regarding animal welfare. As alternatives, bacterial proteins (A and G) have been widely exploited; however, several difficulties are encountered regarding their use for IgG detection and purification. The widespread use of IgGs in the pharmaceutical industry and the increasing number and variety of new Abs entering the market impose the need to develop new detection and purification strategies. The TRIM21 protein is a soluble intracellular IgG receptor that binds to the Fc region of many species with high affinity. We created a chimeric protein containing a mutated form of the C-terminal domain of mouse TRIM21 linked to a streptavidin moiety to detect IgGs from a wide range of species. The protein is promptly produced by heterologous expression and consists of an improved molecular tool, expanding the portfolio of Ab-affinity ligands for immunoassays.