Selective Translocation of Cyclic Sugars through Dynamic Bacterial Transporter

The selective translocation of molecules through membrane pores is an integral process in cells. We present a bacterial sugar transporter, CymA of unusual structural conformation due to a dynamic N terminus segment in the pore, reducing its diameter. We quantified the translocation kinetics of various cyclic sugars of different charge, size, and symmetry across native and truncated CymA devoid of the N terminus using single-channel recordings. The chemically divergent cyclic hexasaccharides bind to the native and truncated pore with high affinity and trans-locate effectively. Specifically, these sugars bind and translocate rapidly through truncated CymA compared to native CymA. In contrast, larger cyclic heptasaccharides and octasaccharides do not translocate but bind to native and truncated CymA with distinct binding kinetics highlighting the importance of molecular charge, size and symmetry in translocation consistent with liposome assays. Based on the sugar-binding kinetics, we suggest that the N terminus most likely resides inside the native CymA barrel, regulating the transport rate of cyclic sugars. Finally, we present native CymA as a large nanopore sensor for the simultaneous single-molecule detection of various sugars at high resolution, establishing its functional versatility. This natural pore is expected to have several applications in nanobiotechnology and will help further our understanding of the fundamental mechanism of molecular transport.

Automated summary

Selective translocation of molecules through membrane pores is crucial in cells. This study focuses on the bacterial sugar transporter CymA, which has an unusual structural conformation due to a dynamic N terminus segment. The researchers found that cyclic hexa-saccharides can effectively translocate across native and truncated CymA, while larger cyclic hepta-saccharides and octa-saccharides cannot. Based on the sugar-binding kinetics, the N terminus is proposed to regulate the transport rate of cyclic sugars inside the native CymA barrel. Additionally, this study presents native CymA as a versatile nanopore sensor for high-resolution single-molecule detection of various sugars.