Predicted to enable endopeptidase activator activity; enzyme binding activity; and identical protein binding activity. Acts upstream of or within several processes, including negative regulation of CD4-positive, alpha-beta T cell proliferation; negative regulation of T cell cytokine production; and positive regulation of BMP signaling pathway. Located in external side of plasma membrane. Is expressed in several structures, including heart; immune system; lung; male reproductive gland or organ; and small intestine lamina propria. Orthologous to human VSIR (V-set immunoregulatory receptor). [provided by Alliance of Genome Resources, Apr 2022]