Structuraland Functionalstudy Of The D-xylose:H+Sympoter Originated From E.coli

Sugar metabolism affects every aspect of life,and glucose metabolism is the most essential.Cells uptake sugar by sugar porters located on the cell membrane.There are two categories of glucose transporters in human,which relate to multiple physiological and pathological activities.We choose one category named GLUT family and their bacterial homologue XylE as research targets.The Escherichia coli D-xylose:H+ symporter XylE sharesapproximately 50% sequence similarities of Class I GLUTs,and is specifically capble of D-xylose transport.Tranport activity of XylE is driven by proton and inhibited by D-glucose,while Class I GLUTs need no extra energy for glucose tranport.These facts suggest their tranport mechanisms remain some differences.For further understanding of the transport mechanism,we obtain the 3D crystal structures of XylE separately binding D-xylose,D-glucose and a synthesized bromide derivative of glucose,with resolutions of 2.8?,2.9? and 2.6? respectively.These XylE structures represent almost the same classical 12-transmembrane-helice MFS fold,but with an extra 4-helice intracellular domain and an outward-facing,partially occluded conformation.Structure analysis and biochemical assays help us identify the key residues responsible for substrate recognition in XylE.We further map some disease-related mutations of Class I GLUTs in the structure-based computational modeling of human GLUT1,which enlights primary pathologystudies.The sequence alignment of Xyl E and Class I GLUTs and biochemical experiment results indicate that the Asp27 residue of XylE may be critical in proton coupling.We also designed sequence-based point mutations,in order to convert XylE to a glucose transporter to certain degree.These researches help us further understand the transport mechanism of sugar porters and common features of MFS,and provide a solid base for further study of GLUT family.