A conserved interdomain linker of CCT mediates allosteric communication between regulatory and catalytic domains

Folding landscapes of linkers between ligand-binding and functional domains evolved to facilitate transmission of inter-domain signals. I investigated the structure/function of a conserved linker between the catalytic and membrane-binding (M) domains of CCT, which regulates phosphatidylcholine synthesis and activates upon membrane binding. The activity of CCT is very sensitive to mutations in the linker. Recent molecular dynamics simulations revealed that upon removal of auto-inhibitory contacts between the M domain and the active site, the αE helix adjacent to the linker bends toward the active site, bringing the catalytic domain close to the membrane surface. Tryptophan fluorescence quenching revealed that the linker lies superficially on the membrane surface. FRET between engineered tryptophans and vesicles containing Dansyl-Phosphatidylethanolamine support a bent αE helix conformation that is dependent on the native linker sequence. The data suggests that the linker may communicate membrane binding signals to enhance CCT activity by directly stabilizing a bent αE.