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

Area of Science:

• Structural biology
• Molecular biology
• Biochemistry

Background:

• The Bcl-2 protein family plays a crucial role in regulating programmed cell death.
• The precise mechanism by which Bcl-2 family proteins exert their function remains largely unknown.

Purpose of the Study:

• To elucidate the structural characteristics of Bcl-xL, a key member of the Bcl-2 protein family.
• To investigate the structural basis for the anti-apoptotic activity of Bcl-xL.

Main Methods:

• X-ray crystallography to determine the high-resolution crystal structure of Bcl-xL.
• Solution structure analysis to complement crystallographic data.
• Analysis of protein secondary and tertiary structures, including alpha-helical arrangements and hydrophobic regions.

Main Results:

• The crystal and solution structures of Bcl-xL were determined, revealing a core of two central hydrophobic alpha-helices surrounded by amphipathic helices.
• A flexible 60-residue loop connecting helices alpha1 and alpha2 was identified and found to be non-essential for anti-apoptotic activity.
• The functionally critical Bcl-2 homology regions (BH1, BH2, and BH3) are spatially proximate, forming an elongated hydrophobic cleft potentially serving as a binding site for other Bcl-2 family members.

Conclusions:

• The determined structure of Bcl-xL provides insights into its molecular organization.
• The identified hydrophobic cleft suggests a potential interaction interface for other Bcl-2 family proteins, shedding light on their oligomerization or binding mechanisms.
• The structural resemblance of Bcl-xL to membrane translocation domains of bacterial toxins offers a novel perspective on the potential mechanism of action of the Bcl-2 family in regulating cell death.