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X-ray and NMR structure of human Bcl-xL, an inhibitor of programmed cell death

AUTHORS

Muchmore SW , Sattler M , Liang H , Meadows RP , Harlan JE , Yoon HS , Nettesheim D , Chang BS , Thompson CB , Wong SL , Ng SL , Fesik SW . Nature. 1996 5 23; 381(6580). 335-341

ABSTRACT

The Bcl-2 family of proteins regulate programmed cell death by an unknown mechanism. Here we describe the crystal and solution structures of a Bcl-2 family member, Bcl-xL (ref. 2). The structures consist of two central, primarily hydrophobic alpha-helices, which are surrounded by amphipathic helices. A 60-residue loop connecting helices alpha1 and alpha2 was found to be flexible and non-essential for anti-apoptotic activity. The three functionally important Bcl-2 homology regions (BH1, BH2 and BH3) are in close spatial proximity and form an elongated hydrophobic cleft that may represent the binding site for other Bcl-2 family members. The arrangement of the alpha-helices in Bcl-xL is reminiscent of the membrane translocation domain of bacterial toxins, in particular diphtheria toxin and the colicins. The structural similarity may provide a clue to the mechanism of action of the Bcl-2 family of proteins.