The membrane transporter lactose permease increases lipid bilayer bending rigidity

Abstract

Cellular life relies on membranes, which provide a resilient and adaptive cell boundary. Many essential processes depend upon the ease with which the membrane is able to deform and bend, features that can be characterized by the bending rigidity. Quantitative investigations of such mechanical properties of biological membranes have primarily been undertaken in solely lipid bilayers and frequently in the absence of buffers. In contrast, much less is known about the influence of integral membrane proteins on bending rigidity under physiological conditions. We focus on an exemplar member of the ubiquitous major facilitator superfamily of transporters and assess the influence of lactose permease on the bending rigidity of lipid bilayers. Fluctuation analysis of giant unilamellar vesicles (GUVs) is a useful means to measure bending rigidity. We find that using a hydrogel substrate produces GUVs that are well suited to fluctuation analysis. Moreover, the hydrogel method is amenable to both physiological salt concentrations and anionic lipids, which are important to mimic key aspects of the native lactose permease membrane. Varying the fraction of the anionic lipid in the lipid mixture DOPC/DOPE/DOPG allows us to assess the dependence of membrane bending rigidity on the topology and concentration of an integral membrane protein in the lipid bilayer of GUVs. The bending rigidity gradually increases with the incorporation of lactose permease, but there is no further increase with greater amounts of the protein in the membrane.

A review on the measurement of the bending rigidity of lipid membranes

“…The influence of integral membrane proteins, such as lactose permease (LacY), egg lecithin (EYPC), and N-terminal low complexity domain of fused in sarcoma (FUS LC), on the bending rigidity of lipid bilayers under physiological conditions was investigated. 17,171 Regardless of the ionic strength, the bending rigidity of the membrane containing LacY was higher than that of the membrane without LacY. In Fig.…”

“…15(B), it is clear that the bending rigidity of the membrane containing LacY increased significantly, going from 25 k B T (in the absence of LacY) to a value above 40 k B T , specifically, the value is 43 k B T for PBS 40 : 40 : 20 and 41 k B T for NaPhos 40 : 40 : 20 when LacY is present in the membrane. 17…”

“…15(B), it is clear that the bending rigidity of the membrane containing LacY increased significantly, going from 25k B T (in the absence of LacY) to a value above 40k B T, specifically, the value is 43k B T for PBS 40 : 40 : 20 and 41k B T for NaPhos 40 : 40 : 20 when LacY is present in the membrane. 17 The bending rigidity was found to increase and eventually saturate with increasing mole fraction of polyethylene glycol (PEG)-grafted lipid. [172][173][174] Also, the rise in bending rigidity was more pronounced, and the saturation values for low mol% of PEG vesicles were significantly higher for GUVs synthesized with longer PEG chain lengths.…”

“…13 But, the bending stiffness demonstrated the opposite phenomena in the case of changing salt concentration. 13,14 The membrane rigidity can also be strongly modulated by peptides, 15,16 proteins, 17 polysaccharides, 18 and different sterols. 19 Due to the progressively wide expansion of research in membrane biophysics, it is necessary to provide up-todate information on the physical properties of biomembranes and lipid bilayers to the scientific community.…”

Cellular journey of nanomaterials: Theories, trafficking, and kinetics

“…Usually, these proteins embedded in the plasma membrane could serve as specific receptors for binding NMs, or form specific domains which strengthen the rigidity of plasma membrane. [38] Wang et al reported that artificial phospholipid bilayer might capture the electrostatic interaction with similar responses as plasma membranes, but the integrity of artificial phospholipid bilayer is much more vulnerable than the plasma membrane. [39] After the adsorption of NMs on the plasma membrane, the adhesion strength needs to go over the energy barrier composed of binding energy and stretching energy to drive the internalization of NMs.…”