Effects of chelator lipids, paramagnetic metal ions and trehalose on liposomes by solid-state NMR.

The effects of various lipid bound paramagnetic metal ions on liposomes prepared in the presence of trehalose and chelator lipids are evaluated to observe site-specific signal changes on liposome samples with optimal resolution in solid-state NMR spectroscopy. We found that Mn2+, Gd3+ and Dy3+ have different influences on the lipid 13C sites depending on their penetration depths into the bilayer, which can be extracted as distance information. The trehalose-liposome mixture is efficiently packed into solid-state NMR rotors and provides optimal resolution at reasonable instrument temperatures (10-50 °C). The effectiveness and convenience of the trehalose preparation for studying a membrane protein in liposomes are demonstrated by a membrane sample with a model membrane peptide to show that trehalose is useful to prepare consistent and stable membrane protein liposome samples for solid-state NMR.

An oligopeptide transporter gene family in Arabidopsis.

We have identified nine oligopeptide transporter (OPT) orthologs (AtOPT1 to AtOPT9) in Arabidopsis. These proteins show significant sequence similarity to OPTs of Candida albicans (CaOpt1p), Schizosaccharomyces pombe (Isp4p), and Saccharomyces cerevisiae (Opt1p and Opt2p). Hydrophilicity plots of the OPTs suggest that they are integral membrane proteins with 12 to 14 transmembrane domains. Sequence comparisons showed that the AtOPTs form a distinct subfamily when compared with the fungal OPTs. Two highly conserved motifs (NPG and KIPPR) were found among all OPT members. The identification of multiple OPTs in Arabidopsis suggests that they may play different functional roles. This idea is supported by the fact that AtOPTs have a distinct, tissue-specific expression pattern. The cDNAs encoding seven of the AtOPTs were cloned into a yeast vector under the control of a constitutive promoter. AtOPT4 expressed in S. cerevisiae mediated the uptake of KLG-[3H]L. Similarly, expression of five of the seven AtOPT proteins expressed in yeast conferred the ability to uptake tetra- and pentapeptides as measured by growth. This study provides new evidence for multiple peptide transporter systems in Arabidopsis, suggesting an important physiological role for small peptides in plants.