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

demonstrates that weakening the sealability of the SecY channel allowed free diffusion of 23 sugars, including glucose, fructose, mannose, xylose, arabinose, and lactose, into the 24 engineered cells, facilitating its rapid growth on a wide spectrum of monosaccharides and 25 bypassing/reducing stereospecificity, transport saturation, competitive inhibition, and (Cirillo, 1961; Reinhold & Kaplan, 1984; Chen et al, 2015) . Active transport requires 40 metabolic energy to passage molecules across the plasma membrane in the direction 41 against the concentration gradient, whereas passive transport moves molecules down its 42 concentration without needing an energy input, which can be further classified as 43 facilitated diffusion and free diffusion, respectively. Active transport and facilitated 44 diffusion are dependent on the specific molecular binding between cargo and transporter, 45 thereby exhibiting stereospecificity, transport saturation, and competitive inhibition 46 (Cirillo, 1961) . Moreover, numerous sugars are taken up with concomitant 47 phosphorylation via the phosphoenolpyruvate (PEP): carbohydrate phosphotransferase 48 system (PTS), which may cause carbon catabolite repression (CCR), leading to a diauxic 49 cell growth (Stülke & Hillen, 1999) . Fig 1A illustrates the main transporters of glucose, 50 fructose, mannose, xylose, arabinose, and lactose in Escherichia coli, a Gram-negative, 51 facultatively anaerobic bacterium. In contrast, free diffusion is a non-mediated transport 52 with a linear rate in proportion to the concentration difference. However, it is believed 53 that only small, non-polar molecules, such as carbon dioxide and oxygen, can freely 54 diffuse through the plasma membrane (Zhao et al, 2011). Therefore, although many 55 All rights reserved. No reuse allowed without permission.