Size and Orientation of the Lipid II Headgroup As Revealed by AFM Imaging

Abstract

In this study, we investigated the size and orientation of the bacterial Lipid II (L II) headgroup when the L II molecule is present in liquid-crystalline domains of DOPC in a supported DPPC bilayer. Using atomic force microscopy, we detected that L II causes the appearance of a 1.9 nm thick layer, situated over the DOPC headgroup region. With an increased scanning force, this layer can be penetrated by the AFM tip down to the level of the DOPC bilayer. Using different L II precursor molecules, we demonstrated that the detected layer consists of the headgroups of L II and that the MurNAc-pentapeptide unit of the headgroup is responsible for the measured 1.9 nm height of that layer. Monolayer experiments provided information about the in-plane dimensions of the L II headgroup. On the basis of these results and considerations of the molecular dimensions of L II headgroup constituents, we propose a model for the orientation of the L II headgroup in the membrane. In this model, the pentapeptide of the L II headgroup is rather extended and points away from the bilayer surface, which could be important for biological processes, in which L II is involved.

Daptomycin inhibits cell envelope synthesis by interfering with fluid membrane microdomains

“…Interestingly, it has been shown that fluorescently labeled vancomycin, which binds lipid II, localizes to the strongly fluorescent membrane patches induced by daptomycin (22), indicating the presence of lipid II in these arrested fluid lipiddaptomycin clusters. Lipid II is likely to accumulate at RIFs, because its long bactoprenol moiety prefers a fluid lipid environment (56). These observations are in good agreement with our finding that MurG preferentially binds to RIFs and further supports the notion that RIFs are membrane microdomains associated with lateral cell wall biosynthesis (38,57,58).…”

Lipid II: A central component in bacterial cell wall synthesis and a target for antibiotics

“…Incorporation of Lipid II in supported bilayers of phosphatidylcholine revealed that the bactoprenol chain must be fluid, because Lipid II partitions in fluid domains, present in mixed solid/fluid bilayers. This was observed by atomic force microscopy (AFM) using the lantibiotic nisin, which binds specifically to Lipid II to visualize its location [3]. Consistent with this finding was the observation made by confocal fluorescence microscopy that NBD-labeled Lipid II was homogeneously distributed in GUVs of DOPC [4].…”

“…The AFM technique also revealed that the head group of Lipid II is soft and can be penetrated by the AFM probe [3]. This property of the molecule allowed insight into the dimensions of the head group, which was estimated to be 1.9 nm high as compared to the level of the phospholipid head group [3].…”

“…This property of the molecule allowed insight into the dimensions of the head group, which was estimated to be 1.9 nm high as compared to the level of the phospholipid head group [3]. Given that the limiting area of the head group is 1.5 nm 2 as observed in monolayer studies, the pentapeptide must have an upright position and be fully accessible to the aqueous phase [3]. Another intriguing property of Lipid II and several of its precursors is that it displays a pyrophosphate in the membrane interface.…”

Determinants of Bacterial Morphology: From Fundamentals to Possibilities for Antimicrobial Targeting

“…Indeed, E. coli minicells, in which a very high percentage of the membrane is in a highly curved state, are enriched in cardiolipin (Koppelman et al, 2001). Thus, the effect of membrane composition on cell shape might be indirect, such as by affecting the localization of lipid II or MreB, which are both linked to specific membrane organization (Ganchev et al, 2006; Strahl et al, 2014). …”