Differentiation of gram-negative intermembrane phospholipid transporter function by intrinsic substrate preference.

. TamB also modulates phospholipid transport in a distantly related diderm Fermicute. Here, we investigate functional differentiation between YhdP and TamB. Our data strongly suggest YhdP's and TamB's functions are distinguished by the saturation state of phospholipids with YhdP preferentially transporting more saturated phospholipids and TamB transporting more unsaturated phospholipids. Cardiolipin headgroup specificity may also contribute to TamB inhibition, perhaps due to the bulky nature of cardiolipin inhibiting the passage of other phospholipids. Diversification of function between YhdP and TamB provides a mechanism for regulation of phospholipid composition, and possibly the mechanical strength and permeability of the outer membrane, and so the cell's intrinsic antibiotic resistance, in changing environmental conditions.