On the interaction between lipopolysaccharide-specific LA27 aptamer and bacterial-mimicking lipid bilayers: Neutron Reflectometry Study

Gram(-) bacteria are pathogenic microorganisms whose outer membrane of the external envelope is composed of complex molecules, such as lipopolysaccharides (LPS), consisting of three structural domains: lipid A, the core oligosaccharide and the O antigen. They are considered endotoxins responsible for many infections induced by bacterial pathogens, so they represent a suitable target for selective detection of their presence in aqueous environment. Selective LPS detection can be achieved through specifically designed biosensors, exploiting the biological response deriving from the biorecognition molecule and the analyte into a measurable signal. Among biorecognition molecules, aptamers are very appealing. They are single-stranded oligonucleotides with high affinity and specificity towards specific analytes. Recently, a small aptamer, LA27, has been identified to selectively recognise LPS. The LPS portion interacting with LA27 is not well-understood yet, although preliminary studies suggest an affinity with lipid A. In this context, we performed a biophysical investigation on the interaction of LA27 biorecognition molecule with asymmetric Supported Lipid Bilayers (SLBs) prepared by the Langmuir-Blodgett method: the outer leaflet was composed by the deuterated di-palmitoyl-phosphocholine (d-DPPC), while three LPS extracted from three different Gram(-) strains, such as Akkermansia, Flavobacterium and Paenalcaligenes hominis respectively, were used to form the outer leaflet of the biomimicking bacterial membranes. The study was carried out for each of these samples at 25 °C and 38 °C in the presence of various solvent contrasts by means of Neutron Reflectometry. This analysis allowed us to shed light on the binding affinity of LA27 with a specific portion of LPS.