Dynamics and Molecular Interactions of GPI-Anchored CD59

Area of Science:

• Immunology
• Structural Biology
• Biophysics

Background:

• CD59 is a crucial cell surface receptor that inhibits the complement membrane attack complex (MAC), preventing cell damage.
• Despite its inhibitory role, CD59 is exploited by bacterial pore-forming proteins to target host cells.
• Previous studies revealed varied orientations of CD59's ectodomain when bound to different partners.

Purpose of the Study:

• To elucidate the mechanism by which GPI-anchored CD59 accommodates diverse binding modes.
• To identify specific interactions between CD59, complement proteins, and bacterial virulence factors.
• To understand the structural basis for CD59's dual role in innate immunity and pathogen interaction.

Main Methods:

• Coarse-grain molecular dynamics simulations of CD59-inhibited MAC using PyLipID.
• Atomistic simulations of GPI-anchored CD59 utilizing MDAnalysis package.
• Analysis of protein-lipid interactions and CD59 ectodomain flexibility.

Main Results:

• Identified specific complement protein residues (C6:Y285, C6:R407, C6:K412, C7:F224, C8β:F202, C8β:K326) interacting with lipids.
• Revealed intrinsic properties of CD59 that confer the necessary flexibility for varied binding.
• Demonstrated how CD59's structure supports interactions with both complement proteins and bacterial pore-forming toxins.

Conclusions:

• GPI-anchored CD59 possesses inherent flexibility enabling diverse binding orientations.
• Specific lipid interactions contribute to the stability and function of CD59 in the MAC pathway.
• CD59's adaptability is key to its function as a complement inhibitor and its susceptibility to bacterial co-option.