自从上个世纪90年代起人们就已经知道，霍乱弧菌（Vibrio cholerae）中的霍乱毒素基因见于结合的噬菌体CTX?中，这个噬菌体位于霍乱弧菌与“toxin-linked cryptic (TLC)”相邻的基因组中，后者是一个功能未知的染色体DNA成分。
现在，TLC被发现相应于TLC的基因组，它是一个“卫星细丝噬菌体”，利用第三个细丝噬菌体(fs2?)的形态发生基因形成感染性颗粒。通过重建导致噬菌体DNA被获取的事件和将这些事件与流行性菌种的基因组相对比，Hassan等人建立了一个模型，该模型反映恶性霍乱弧菌是怎样演化为成功的人类病原体的
Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, CB105, La Jolla, California 92037, USA
Transporter proteins from the MATE (multidrug and toxic compound extrusion)1 family are vital in metabolite transport in plants2, 3, directly affecting crop yields worldwide4. MATE transporters also mediate multiple-drug resistance (MDR) in bacteria and mammals5, modulating the efficacy of many pharmaceutical drugs used in the treatment of a variety of diseases6, 7, 8, 9. MATE transporters couple substrate transport to electrochemical gradients and are the only remaining class of MDR transporters whose structure has not been determined10. Here we report the X-ray structure of the MATE transporter NorM from Vibrio cholerae determined to 3.65??, revealing an outward-facing conformation with two portals open to the outer leaflet of the membrane and a unique topology of the predicted 12 transmembrane helices distinct from any other known MDR transporter. We also report a cation-binding site in close proximity to residues previously deemed critical for transport11. This conformation probably represents a stage of the transport cycle with high affinity for monovalent cations and low affinity for substrates
