Structural characterization of the interactions between Lipid II and phospholipid membranes

Abstract

Lipid II (LII) is a component of the bacterial cytoplasmic membrane. Even when it is present in a minor proportion, it is responsible for the fast growing of the bacterial cell wall. It is a central component of the enzymatic cell wall building machinery, translocating the monomeric peptidoglycan units from the cytoplasm to the membrane outside. LII consists of a pentapeptide chain bound to a monomeric peptidoglycan unit, with a long undecaprenyl (bactoprenol) hydrocarbon chain that is coupled through a pyrophosphate linker. Due to its function, LII represents a primary molecular target for a large number of antibiotics.(1)We studied the interactions of LII in model lipid membranes containing dipalmitoylphosphatidylglycerol (DPPG) and dipalmitoylphosphatidylcholine (DPPC) using Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). Pure LII displayed an amide I´ infrared absorption band with two componentes: at 1644 cm-1 assigned to unordered structure and at 1628 cm-1 assigned to border beta strand. In mixtures with phospholipids the spectral shape remained unchanged. Pure LII did not show a cooperative heat absorption within the temperature range 5 - 70 C. In mixtures with dipalmitoylphospholipids, even at the small proportion of 2%, produced the disappearance of the phospholipid pre-transition. The temperature for the gel to liquid phase transition remained constant also at larger proportions of LII.