Seed storage protein. Accumulates during seed development and is hydrolyzed after germination to provide a carbon and nitrogen source for the developing seedling. The alpha-, alpha'-, and beta-subunits associate in various combinations to form trimeric proteins. Localizes in protein storage vacuoles in cotyledons of developing and mature beans (PubMed:15447650). Synthesized and assembled into trimers in the endoplasmic reticulum, and transported to the protein storage vacuoles by the dense vesicles (PubMed:15447650). Causes an allergic reaction in human (PubMed:18996574). Binds to IgE of patients with severe allergic reactions (anaphylaxis) to soybean (PubMed:18996574). Belongs to the 7S seed storage protein family.