Evidence for direct squalene and 2,3-oxidosqualene binding by supernatant protein factor

We present the crystal structures of the SEC14-like domain of supernatant protein factor (SPF) in complex with squalene and 2,3-oxidosqualene. The structures were resolved at 1.75 Å (complex with squalene) and 1.6 Å resolution (complex with 2,3-oxidosqualene), leading in both cases to clear images of the protein/ substrate interactions. Ligand binding is facilitated by removal of the Golgi-dynamics (GOLD) C-terminal domain of SPF, which, as shown in previous structures of the apo-protein, blocked the opening of the binding pocket to the exterior. Both substrates bind into a large hydrophobic cavity, typical of such lipid-transporter family. Our structures report no specific recognition mode for the epoxide group. In fact, for both molecules, ligand affinity is dominated by hydrophobic interactions, and independent investigations by computational models or differential scanning micro-calorimetry reveal similar binding affinities for both ligands. Our findings elucidate the molecular bases of the role of SPF in sterol endo-synthesis, supporting the original hypothesis that SPF is a facilitator of substrate flow within the sterol synthetic pathway. Moreover, our results suggest that the GOLD domain acts as a regulator, as its conformational displacement must occur to favor ligand binding and release during the different synthetic steps.

水稻2,3-氧化鲨烯环化酶基因的功能研究

植物通过异戊二烯代谢途径合成多种具有生物活性和功能的三萜及甾醇类化合物，它们在调节植物生长发育、维持膜的完整和功能、抵抗病原微生物侵染中发挥着重要的作用。2,3-氧化鲨烯为三萜和甾醇合成途径的分枝点，参与这一关键步骤的酶被通称为2,3-氧化鲨烯环化酶（OSCs）。本研究系统分了水稻基因组中全部11个OSC基因序列，发现其中四个可能为假基因。亚种间非同义替换率Ka和同义替换率Ks的比值（Ka/Ks）以及进化树的分析表明OsOSC8是单子叶植物特有的功能保守基因，而OsOSC9在水稻两个亚种间发生了功能快速进化，这种快速进化的基因往往参与植物和病原菌相互作用的代谢途径。 根据基因结构、表达谱以及与其它植物已知功能的OSC酶氨基酸序列的比对推测OsOSC3可能具有环阿屯醇合成酶的功能，参与植物甾醇的合成，而OsOSC7、OsOSC10和OsOSC11可能具有β-香树素合成酶的功能，其余OSCs可能参与合成其它三萜化合物。为了进一步分析和验证OSCs酶的功能，将水稻7个OSC基因的开放阅读框（ORF）构建到酵母表达载体并在pichia酵母中表达，发现仅有OsOSC9和OsOSC12能够将酵母内源的2,3-氧化鲨烯分别环化为四环三萜化合物Parkeol和植物中稀有的五环三萜化合物Isoarborinol，目前还未在其它植物中发现参与这两种三萜化合物的基因。另外，水稻所有的OSC基因均不能互补酵母羊毛甾醇缺陷型菌株，表明水稻OSCs不具有合成羊毛甾醇的功能。 RNAi沉默以及启动子融合GUS的表达实验发现OsOSC8可能参与花粉的发育，该基因的下调影响水稻的育性，暗示水稻中存在一个可能与雄性不育有关的三萜代谢途径。水稻其它OSC基因RNAi植株可能在逆境环境和病原菌侵染下才会显现出表型。

Molecular cloning, characterization, and functional expression of rat oxidosqualene cyclase cDNA.

A cDNA encoding rat oxidosqualene lanosterol-cyclase [lanosterol synthase; (S)-2,3-epoxysqualene mutase (cyclizing, lanosterol-forming), EC 5.4.99.7] was cloned and sequenced by a combination of PCR amplification, using primers based on internal amino acid sequence of the purified enzyme, and cDNA library screening by oligonucleotide hybridization. An open reading frame of 2199 bp encodes a M(r) 83,321 protein with 733 amino acids. The deduced amino acid sequence of the rat enzyme showed significant homology to the known oxidosqualene cyclases (OSCs) from yeast and plant (39-44% identity) and still retained 17-26% identity to two bacterial squalene cyclases (EC 5.4.99.-). Like other cyclases, the rat enzyme is rich in aromatic amino acids and contains five so-called QW motifs, highly conserved regions with a repetitive beta-strand turn motif. The binding site sequence for the 29-methylidene-2,3-oxidosqualene (29-MOS), a mechanism-based irreversible inhibitor specific for the vertebrate cyclase, is well-conserved in all known OSCs. The hydropathy plot revealed a rather hydrophilic N-terminal region and the absence of a hydrophobic signal peptide. Unexpectedly, this microsomal membrane-associated enzyme showed no clearly delineated transmembrane domain. A full-length cDNA was constructed and subcloned into a pYEUra3 plasmid, selected in Escherichia coli cells, and used to transform the OSC-deficient uracil-auxotrophic SGL9 strain of Saccharomyces cerevisiae. The recombinant rat OSC expressed was efficiently labeled by the mechanism-based inhibitor [3H]29-MOS.

A new low temperature synthesis route of fraipontite (Zn,Al)3(Si,Al)2O5(OH)4

A low temperature synthesis method based on the decomposition of urea at 90°C in water has been developed to synthesise fraipontite. This material is characterised by a basal reflection 001 at 7.44 Å. The trioctahedral nature of the fraipontite is shown by the presence of a 06l band around 1.54 Å, while a minor band around 1.51 Å indicates some cation ordering between Zn and Al resulting in Al-rich areas with a more dioctahedral nature. TEM and IR indicate that no separate kaolinite phase is present. An increase in the Al content however, did result in the formation of some SiO2 in the form of quartz. Minor impurities of carbonate salts were observed during the synthesis caused by to the formation of CO32- during the decomposition of urea.

Vibrational spectroscopy of phthalocyanine and naphthalocyanine in sandwich-type (na)phthalocyaninato and porphyrinato rare earth complexes: Part 14. The infrared and Raman characteristics of phthalocyanine in “pinwheel-like” homoleptic bis[1,8,15,22-tetrakis(3-pentyloxy)phthalocyaninato] rare earth(III) double-decker complexes

The infrared (IR) spectroscopic data and Raman spectroscopic properties for a series of 13 “pinwheel-like” homoleptic bis(phthalocyaninato) rare earth complexes M[Pc(α-OC5H11)4]2 [M = Y and Pr–Lu except Pm; H2Pc(α-OC5H11)4 = 1,8,15,22-tetrakis(3-pentyloxy)phthalocyanine] have been collected and comparatively studied. Both the IR and Raman spectra for M[Pc(α-OC5H11)4]2 are more complicated than those of homoleptic bis(phthalocyaninato) rare earth analogues, namely M(Pc)2 and M[Pc(OC8H17)8]2, but resemble (for IR) or are a bit more complicated (for Raman) than those of heteroleptic counterparts M(Pc)[Pc(α-OC5H11)4], revealing the decreased molecular symmetry of these double-decker compounds, namely S8. Except for the obvious splitting of the isoindole breathing band at 1110–1123 cm−1, the IR spectra of M[Pc(α-OC5H11)4]2 are quite similar to those of corresponding M(Pc)[Pc(α-OC5H11)4] and therefore are similarly assigned. With laser excitation at 633 nm, Raman bands derived from isoindole ring and aza stretchings in the range of 1300–1600 cm−1 are selectively intensified. The IR spectra reveal that the frequencies of pyrrole stretching and pyrrole stretching coupled with the symmetrical CH bending of –CH3 groups are sensitive to the rare earth ionic size, while the Raman technique shows that the bands due to the isoindole stretchings and the coupled pyrrole and aza stretchings are similarly affected. Nevertheless, the phthalocyanine monoanion radical Pc′− IR marker band of bis(phthalocyaninato) complexes involving the same rare earth ion is found to shift to lower energy in the order M(Pc)2 > M(Pc)[Pc(α-OC5H11)4] > M[Pc(α-OC5H11)4]2, revealing the weakened π–π interaction between the two phthalocyanine rings in the same order.