Apoptosis is known or suspected to contribute to acute diseases,such as stroke,heart attack and liver failure,through inducing massive cell death in tissues or organs,and to certain slow-progressing diseases,such as Parkinsons disease.As almost all cells of our body are equipped with apoptosis machinery,it is an attractive target for therapeutic intervention.A powerful anti-apoptotic agent would be useful for medical applications for many diseases by protecting cells.from unwanted cell death.We determined the refined crystal structure of Bcl-xL,an anti-apoptotie member of the Bcl-2 family,and found that Bcl-XL has nine intrarmolecular polar interactions to stabilize the central pore-forming domain.