Glycerol-induced formation of the molten globule from acid-denatured cytochrome c: implication for hierarchical folding

At high concentration (98% or higher, v/v), glycerol induces collapse of acid-denatured cytochrome c into a compact state, the G_U state, showing a molten globule character. The G_U state possesses a nativelike -helix structure but a tertiary conformation less packed with respect to the native state. The spectroscopic properties of the G_U state closely resemble those of the molten globule stabilized by the organic solvent from the native protein (called the G_N state), indicating that glycerol can stabilize the molten globule of cytochrome c either from the native or the acid-denatured protein. The G_U and the G_N states show spectroscopic (and, thus, structural) properties and stabilities comparable to those of molten globules stabilized by different effectors, despite the fact that the mechanisms involved in the molten globule formation may significantly differ. This implies in cytochrome c a hierarchy for the rupture (native-to-molten globule) or the formation (unfolded-to-molten globule) of intramolecular interactions leading to the stabilization of the molten globule state of the protein, independently from the effector responsible for the structural transition, in accord with the sequential model proposed by Englander and collaborators.     

Continuous cultures of Clostridium acetobutylicum: culture stability and low-grade glycerol utilisation

Continuous cultures of two strains of Clostridium acetobutylicum were stable for over 70 d when grown on glucose/glycerol mixtures. Butanol was the major fermentation end-product, accounting for 43 to 62% (w/w) of total products. Low-grade glycerol [65% (w/v) purity] could replace commercial glycerol [87% (w/v) purity], leading to a similar fermentation pattern: a butanol yield of 0.34 (mol/mol), a butanol productivity of 0.42 g l^–1 h^–1 and a 84% (w/w) glycerol consumption were attained when cultures were grown at pH 6 and D = 0.05 h^–1; butanol accounted for 94% (w/w) of total solvents. These values are among the highest reported in literature for C. acetobutylicum simple chemostats.     

Angiostatin production in cultivation of recombinant Pichia pastoris fed with mixed carbon sources

A recombinant strain of Pichia pastoris with a phenotype of Mut^S was used to produce angiostatin. Due to the low methanol consumption rate of this strain, both methanol and glycerol feedings, that produced oscillation in dissolved O₂ concentration, were used during the expression phase to improve cell growth and angiostatin expression. However, enhanced cell growth led to nitrogen limitation that suppressed further production of angiostatin, but addition of ammonia allowed angiostatin concentration to reach 108 mg l^–1 after an expression period of 96 h. The ratio of consumed glycerol to methanol of 1.5:1 (w/w) in the expression phase suggested that methanol played an important role in the metabolism of carbon sources.     

Indole-3-glycerol phosphate, a branchpoint of indole-3-acetic acid biosynthesis from the tryptophan biosynthetic pathway in Arabidopsis thaliana

The phytohormone indole-3-acetic acid (IAA) plays a vital role in plant growth and development as a regulator of numerous biological processes. Its biosynthetic pathways have been studied for decades. Recent genetic and in vitro labeling evidence indicates that IAA in Arabidopsis thaliana and other plants is primarily synthesized from a precursor that is an intermediate in the tryptophan (Trp) biosynthetic pathway. To determine which intermediate(s) acts as the possible branchpoint for the Trp-independent IAA biosynthesis in plants, we took an in vivo approach by generating antisense indole-3-glycerol phosphate synthase (IGS) RNA transgenic plants and using available Arabidopsis Trp biosynthetic pathway mutants trp2-1 and trp3-1. Antisense transgenic plants display some auxin deficient-like phenotypes including small rosettes and reduced fertility. Protein gel blot analysis indicated that IGS expression was greatly reduced in the antisense lines. Quantitative analyses of IAA and Trp content in antisense IGS transgenic plants and Trp biosynthetic mutants revealed striking differences. Compared with wild-type plants, the Trp content in all the transgenic and mutant plants decreased significantly. However, total IAA levels were significantly decreased in antisense IGS transgenic plants, but remarkably increased in trp3-1 and trp2-1 plants. These results suggest that indole-3-glycerol phosphate (IGP) in the Arabidopsis Trp biosynthetic pathway serves as a branchpoint compound in the Trp-independent IAA de novo biosynthetic pathway.     

Prediction of functional residues in water channels and related proteins.

In this paper, we present an updated classification of the ubiquitous MIP (Major Intrinsic Protein) family proteins, including 153 fully or partially sequenced members available in public databases. Presently, about 30 of these proteins have been functionally characterized, exhibiting essentially two distinct types of channel properties: (1) specific water transport by the aquaporins, and (2) small neutral solutes transport, such as glycerol by the glycerol facilitators. Sequence alignments were used to predict amino acids and motifs discriminant in channel specificity. The protein sequences were also analyzed using statistical tools (comparisons of means and correspondence analysis). Five key positions were clearly identified where the residues are specific for each functional subgroup and exhibit high dissimilar physico-chemical properties. Moreover, we have found that the putative channels for small neutral solutes clearly differ from the aquaporins by the amino acid content and the length of predicted loop regions, suggesting a substrate filter function for these loops. From these results, we propose a signature pattern for water transport.     

Two-component signal transduction systems in eukaryotic microorganisms

Conserved signal transduction pathways that use phosphorelay from histidine kinases through an intermediate transfer protein (H2) to response regulators have been found in a variety of eukaryotic microorganisms. Several of these pathways are linked to mitogen-activated protein kinase cascades. These networks control different physiological responses including osmoregulation, cAMP levels and cellular morphogenesis.     

Phospholipids of wheat chloroplast and its membranes under water stress

Phospholipids showed a differential change in the chloroplast membranes in two cultivars under water stress. Amongst the individual phospholipids, phosphatidyl choline (PC) increased under stress in the low water requiring cultivar C-306 but it decreased in high water requiring cultivar S-308. PC of chloroplast envelope and chloroplast thylakoids showed similar response. Increase in PC content in chloroplasts and its membranes of resistant cultivar may suggest a basis for stress resistance.     

Effect of sex,dietary glycerol or dietary fat during late fattening,on fatty acid composition and positional distribution of fatty acids within the triglyceride in pigs

The effect of sex, source of saturated fat (lard v. palm oil) and glycerol inclusion in the fattening diet on composition and fatty acid positional distribution in the triglyceride molecule was studied in pigs from 78 to 110 kg BW. Average daily gain and carcass characteristics, including ham and loin weight, were not affected by dietary treatment but sex affected backfat depth (P<0.01). A significant interaction between sex and glycerol inclusion was observed; dietary glycerol increased lean content in gilts but not in barrows (P<0.05 for the interaction). Individual and total saturated fatty acid (SFA) concentrations were greater in barrows than in gilts. In contrast, the concentration of total polyunsaturated fatty acids (PUFA) and of C18:2n-6, C18:3n-3, C20:3n-9 and C20:4n-6 in the intramuscular fat (IMF) was higher (P<0.05) in gilts than in barrows. Sex did not affect total monounsaturated fatty acids (MUFA) concentration in the IMF. The proportion of SFA in the subcutaneous fat (SF) was higher in barrows than in gilts (P<0.001). Within the individual SFA, sex affected only the concentrations of C14:0 and C16:0 (P<0.001). Dietary fat did not affect total SFA or PUFA concentrations of the IMF but the subcutaneous total MUFA concentration tended to be higher (P=0.079) in pigs fed lard than in pigs fed palm oil. Dietary glycerol increased total MUFA and C18:1n-9 concentration in the IMF and increased total MUFA and decreased C18:2n-6, C18:3n-3 and total PUFA concentrations in the SF. The data indicate that altering the fatty acid composition of the triglyceride molecule at the 2-position, by dietary intervention during the fattening phase, is very limited.     

微生物法生产1,3-二羟基丙酮代谢工程研究进展

1,3-二羟基丙酮是一种重要的化工原料和医药中间体,广泛应用于化妆品、医药、食品等领域。以下综述了微生物法生产1,3-二羟基丙酮的代谢途径和关键酶,以及微生物法生产1,3-二羟基丙酮所涉及的代谢工程技术的研究进展。指出利用基因工程的方法对菌株进行改造,提高甘油脱氢酶催化活性,同时根据菌株的代谢特性,对发酵过程进行调控,提高1,3-二羟基丙酮的得率,是今后的研究方向。