 The proteins are then released from the beads by an enzyme (TEV protease) which breaks the tag at the TEV cleavage site in the middle.After this first purification step, a second type of bead (coated with calmodulin) is added to the released proteins which binds reversibly to the remaining piece of the TAP tag still on the proteins.The beads are again separated by centrifugation, further removing contaminants as well as the TEV protease.