An induced folding process characterizes the partial-loss of function mutant LptAI36D in its interactions with ligands.

Lipopolysaccharide (LPS) is an essential glycolipid of the outer membrane (OM) of Gram-negative bacteria with a tripartite structure: lipid A, oligosaccharide core and O antigen. Seven essential LPS-transport proteins (LptABCDEFG) move LPS to the cell surface. Lpt proteins are linked by structural homology, featuring a β-jellyroll domain that mediates protein-protein interactions and LPS binding. Analysis of LptA-LPS interaction by fluorescence spectroscopy is used here to evaluate the contribution of each LPS moiety in protein-ligand interactions, comparing the wild-type (wt) protein to the I36D mutant. In addition to a crucial role of lipid A, an unexpected contribution emerges for the core region in recognition and binding of Lpt proteins.