水分生理研究进展和植物养分研究进展 植物生理 教学课件.ppt

水分生理研究进展和植物养分研究进展生命科学学院植物生理教研室曹翠玲e-mail: cuilingcao@163.com ? MIP： 　　 Members of the major intrinsic protein (MIP) family form a large and diverse group of membrane proteins that facilitate the bidirectional transport of water and some small solutes across cellular membranes　 (Agre et al., 2002; Thomas et al., 2002). The distribution of MIP: 　　MIPs are widely distributed in organisms from bacteria to higher eukaryotes, and these proteins are especially abundant in plants, with 35 full-length genes present in Arabidopsis. 1.3 nodulin-like MIPs (NIPs)　　The archetype NIP,NOD 26 is located in the peribacteroid membrane (PBM) of soybean nodule cells．1.4 small basic MIPs 　(SIPs)  in Arabidopsis and maize. The SIPs are quite divergent from（区别） the other plant MIPs and show significant sequence differences in loop B where the Asn-Pro-Ala (NPA) box consists of Asn-Pro-Thr or Asn-Pro-Leu. 还可根据水孔蛋白是否对Hg2+敏感Hg2+不敏感型水孔蛋白，如PIP RD28。 特点是无cys残基。Hg2+敏感型水孔蛋白， 如CHIP28。Hg2+抑  制的位点是cys189(在NPA附近)。 ２.结构　　The structures of aquaporin 1 (AQP1), a mammalian water-specific aquaporin, and the Escherichia coli glyceroporin(血型糖蛋白)GlpF have been solved at atomic resolution by x-ray crystallography. The structures show that the overall topologies of these two archetypicalMIPs are remarkably similar, whichsupports the hypothesis that MIP family members share a common ancestor and adopt a common hourglass fold. At the end of each small helix is the highly conserved asparagine–proline–alanine (NPA)　sequence. Each half of the polypeptide　(3·5 helixes) shows significant sequence similarity. The two halves of the polypeptide show obverse symmetry*, with the hydrophobic loops containing the NPA overlapping in the middle of the lipid bilayer to form two hemipores that together create a narrow channel proposed to be similar in shape to an hour-glass. 水通道蛋白单体由一条多肽链组成，分子量为30 kD左右，具有6个跨膜片段。水通道蛋白的N端、C端都