Synthesis of a fluorescent analog for exploring the functions of the bacterial glycopyrophospholipid MPIase

Recent studies have revealed that a glycolipid known as membrane protein integrase (MPIase) plays critical roles in the membrane protein integration and membrane permeabilization in Escherichia coli inner membranes. MPIase constitutes approximately 0.5 % of the inner membrane and is composed of a long glycan, a pyrophosphate linker, and a lipid anchor. However, its low abundance and structural heterogeneity have presented significant challenges in elucidating its mechanisms of action in membrane protein integration and permeabilization. To address these limitations, we have synthesized structurally defined MPIase analogs that retain membrane protein integration activity and uncovered aspects of its mechanism of action. In this study, we have developed a synthetic method for fluorescently labeled MPIase analogs, enabling dynamic studies of MPIase and its interactions with membrane proteins. By exploring various strategies for incorporating amino linkers into the previously synthesized MPIase intermediates, we successfully introduced a fluorescent group into the minimal active structure of MPIase for the first time. This approach provides a versatile platform for synthesizing fluorescent or photoreactive MPIase analogs, offering a powerful tool to advance understanding the functions and roles of MPIase in membrane biology.