Predicted to enable antigen binding activity; protein domain specific binding activity; and ubiquitin protein ligase binding activity. Involved in B cell mediated immunity; CD40 signaling pathway; and cellular calcium ion homeostasis. Acts upstream of or within several processes, including defense response to other organism; positive regulation of B cell activation; and positive regulation of interleukin-12 production. Located in external side of plasma membrane and intracellular membrane-bounded organelle. Part of CD40 receptor complex. Is expressed in several structures, including alimentary system; brain; hemolymphoid system gland; liver and biliary system; and reproductive system. Human ortholog(s) of this gene implicated in several diseases, including Kawasaki disease; autoimmune disease (multiple); end stage renal disease; hyperimmunoglobulin syndrome (multiple); and non-Hodgkin lymphoma (multiple). Orthologous to human CD40 (CD40 molecule). [provided by Alliance of Genome Resources, Apr 2022]