The permeabilized SecY protein-translocation channel can serve as a nonspecific sugar transporter

Sen Mei; Chong Xie; Hao Mi; Chuang Xue; Qiang Guo; Guang-Qing Du; Guo-Bei Li; Cai-Xia Li; Ya-Nan Qu; Ming-Hao Xiong; Yang Jiang; Tian-Wei Tan; Shang-Tian Yang; Li-Hai Fan

When we expressed the SecY with deletion of the plug (SecY (ΔP)) in an E. coli 89 (ΔPtsG) lacking the glucose PTS (Plumbridge, 1998) (Fig 2A and B) , the cell growth 90 defect was not observed (Fig 2D and E) . In contrast, the limited growth on glucose 91 caused by insufficient import of the sole carbon source was partially rescued. We 92 reasoned that the SecY (ΔP) channel might allow glucose to diffuse through the plasma 93 membrane due to its small V A (≈ 0.178 m 3 /kmol) and large diffusion coefficient (D AB ≈ 94 1.009×10 -9 m 2 /s) in water (Appendix Table S1 ), which was confirmed by a [ 14 C]-labelled 95 glucose transport assay (Fig 2C) . With the purpose of further enhancing the glucose 96 uptake, SCVE was co-expressed with the SecY (ΔP) channel (Fig 2A and B) . The SCVE 97 has the ability to permeabilize the outer membrane of E. coli by formation of the 98 transmembrane pores as porins (Liao et al, 2004) . The reduced permeation barrier of the 99 outer membrane might increase the glucose gradient across the SecY (ΔP) channel, thus 100 accelerating the glucose diffusion into the cytoplasm ( Fig 2C) and resulting in a marked 101 All rights reserved. No reuse allowed without permission.