Structural Requirements of a Glycolipid MPIase for Membrane Protein Integration

MPIase is a glycolipid involved in membrane protein integration in the inner membrane of Escherichia coli. To overcome the trace amounts and heterogeneity of natural MPIase, we systematically synthesized MPIase analogs. Structure-activity relationship studies revealed the contribution of distinctive functional groups and the effect of the MPIase glycan length on membrane protein integration activity. In addition, both the synergistic effects of these analogs with the membrane chaperone/insertase YidC, and the chaperone-like activity of the phosphorylated glycan were observed. These results verified the translocon-independent membrane integration mechanism in the inner membrane of E. coli, in which MPIase captures the highly hydrophobic nascent proteins via its characteristic functional groups, prevents protein aggregation, attracts the proteins to the membrane surface, and delivers them to YidC in order to regenerate its own integration activity.

Automated summary

MPIase is a glycolipid involved in membrane protein integration in Escherichia coli's inner membrane. To address the limitations of natural MPIase, we synthesized MPIase analogs and studied their structure-activity relationship. Our findings showed the role of distinctive functional groups and the effect of MPIase glycan length on membrane protein integration activity. Furthermore, we observed the synergistic effects of these analogs with the membrane chaperone/insertase YidC, as well as the chaperone-like activity of the phosphorylated glycan. These results confirm a translocon-independent membrane integration mechanism in E. coli's inner membrane, where MPIase captures hydrophobic nascent proteins, prevents aggregation, attracts proteins to the membrane surface, and delivers them to YidC to regenerate its own integration activity.