Supported phospholipid membrane patches stabilized on graphene surfaces have shown potential in sensor device functionalization, including biosensors and biocatalysis. Lipid dip-pen nanolithography (L-DPN) is a method useful in generating supported membrane structures that maintain lipid functionality, such as exhibiting specific interactions with protein molecules. Here, we have integrated L-DPN, atomic force microscopy, and coarse-grained molecular dynamics simulation methods to characterize the molecular properties of supported lipid membranes (SLMs) on graphene and graphene oxide supports. We observed substantial differences in the topologies of the stabilized lipid structures depending on the nature of the surface (polar graphene oxide vs nonpolar graphene). Furthermore, the addition of water to SLM systems resulted in large-scale reorganization of the lipid structures, with measurable effects on lipid lateral mobility within the supported membranes. We also observed reduced lipid ordering within the supported structures relative to free-standing lipid bilayers, attributed to the strong hydrophobic interactions between the lipids and support. Together, our results provide insight into the molecular effects of graphene and graphene oxide surfaces on lipid bilayer membranes. This will be important in the design of these surfaces for applications such as biosensor devices.

Lipases naturally function at the interface formed between amphiphilic molecules and the aqueous environment. Thermomyces lanuginosus lipase (TLL) is a well-characterised lipase, known to exhibit interfacial activation during which a lid region covering the active site becomes displaced upon interaction with an interface. In this study, we investigate the effect the amino acid sequence of the lid region on interfacial binding and lid dynamics of TLL. Three TLL variants were investigated, a wild-type variant, a variant containing an esterase lid region (Esterase), and a Hybrid variant, containing both wild-type lid residues and esterase lid residues. Multiple coarse-grained molecular dynamics simulations revealed that the interfacial binding orientation of TLL was significantly affected by the nature of amino acids in the lid region, and atomistic simulations indicated effects on the structural dynamics of the lid itself. The atomistic simulations, as well as steered molecular dynamics simulations, also indicated that the Esterase lid region was less flexible than the wild-type lid region, whereas the Hybrid variant displayed superior lid flexibility and stability in the open conformation both at the interface, and in aqueous solution. Additional experiments performed to investigate the activity and binding behaviour of the lipase variants indicated a slightly higher specific activity for the Hybrid variant compared to the wild-type variant, correlating the observations of increased lid flexibility. Together, these results are in line with previous experimental studies, highlighting the importance of the nature of the amino acid residues within the functional lid region of lipases, particularly regarding interfacial binding orientation, activation, and structural stability.

Lipases are enzymes of biotechnological importance that function at the interface formed between hydrophobic and aqueous environments. Hydrophobic interfaces can induce structural transitions in lipases that result in an increase in enzyme activity, although the detailed mechanism of this process is currently not well understood for many lipases. Here, we present a multi-scale molecular dynamics simulation study of how different interfaces affect the conformational dynamics of the psychrophilic lipase M37. Our simulations show that M37 lipase is able to interact both with anionic lipid bilayers and with triglyceride surfaces. Interfacial interactions with triglyceride surfaces promote large-scale motions of the lid region of M37, spanning residues 235–283, revealing an entry pathway to the catalytic site for substrates. Importantly, these results suggest a potential activation mechanism for M37 that deviates from other related enzymes, such as Thermomyces lanuginosus lipase. We also investigated substrate binding in M37 by using steered MD simulations, confirming the open state of this lipase. The exposure of hydrophobic residues within lid and active site flap regions (residues 94–110) during the activation process provides insights into the functional effect of hydrophobic surfaces on lipase activation.

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