Roles for the two N-terminal (β/α) modules in the folding of a (β/α)₈-barrel protein as studied by fragmentation analysis

The (β/α)₈‐barrel is one of the most abundant folds found in enzymes. To identify the independent folding units and the segment(s) that correspond to a minimum core structure within a (β/α)₈‐barrel protein, fragmentation experiments were performed with Escherichia coli phosphoribosylanthranilate isomerase, which has a single (β/α)₈‐barrel domain. Our previous studies indicated that the central four β/α segments comprise an independent folding unit; whereas, the role(s) of the first two β/α segments in folding had not been clarified prior to this report. Herein, we report the design and synthesis of a series of N‐terminally deleted fragments starting with (β/α)_1–5β₆ as the parent construct. Analytical gel filtration and urea‐induced equilibrium unfolding experiments indicated that deletions within the N‐terminal region, that is, within the first two β/α modules, resulted in reduced stability or aggregation of the remaining segments. The (β/α)_3–5β₆ segment appeared to fold into a stable structure and deletion of β₆ from (β/α)_3–5β₆ yielded (β/α)_3–5, which did not form native‐like secondary structures. However, urea‐induced unfolding of (β/α)_3–5, monitored by reduction of tryptophan fluorescence, indicated that the fragment contained a loosely packed hydrophobic core. Taken together, the results of our previous and present fragmentation experiments suggest the importance of the central (β/α)_3–4β₅ module in folding, which is a finding that is compatible with our simulated unfolding study performed previously. Proteins 2010. © 2010 Wiley‐Liss, Inc.     

Endothelin-1 induces p66Shc activation through EGF receptor transactivation: Role of β1Pix/Gαi3 interaction

Endothelin-1 (ET-1) is a vasoconstrictor peptide known to be a potent mitogen for glomerular mesangial cells. We have shown that ET-1 stimulates the adaptor protein p66Shc through Rac/Cdc42 guanine nucleotide exchange factor β₁Pix. In this study, we demonstrate that ET-1-induced serine phosphorylation of p66Shc is mediated through Gα_i3. Pertussis toxin treatment of cells induced a significant decrease in the interaction between β₁Pix and ET_A-R, and an increase in the binding of Gα_i3 and G_β1 to β₁Pix. Activation of heterotrimeric G proteins by AlF₄^? resulted in an increase of Gα_i3 binding to β₁Pix, which was significantly disrupted in cells expressing β₁Pix dimerization deficient mutant, β₁PixΔ (602-611). In cells expressing β₁PixΔ (602-611), ET-1-induced p66Shc activation was also significantly decreased. Specific inhibition of EGF receptor by AG1478 blocked ET-1-induced p66Shc activation and the binding of p66Shc and Gα_i3 to β₁Pix. Inhibition of Erk1/2 blocked p66Shc activation induced by ET-1. Altogether, our results indicate that ET-1 activates p66Shc through EGF receptor transactivation, leading to the activation of Gα_i3, β₁Pix and Erk1/2.     

Toward the molecular basis of inherited prion diseases: NMR structure of the human prion protein with V210I mutation

The development of transmissible spongiform encephalopathies (TSEs) is associated with the conversion of the cellular prion protein (PrP^C) into a misfolded, pathogenic isoform (PrP^Sc). Spontaneous generation of PrP^Sc in inherited forms of disease is caused by mutations in gene coding for PrP (PRNP). In this work, we describe the NMR solution-state structure of the truncated recombinant human PrP (HuPrP) carrying the pathological V210I mutation linked to genetic Creutzfeldt-Jakob disease. The three-dimensional structure of V210I mutant consists of an unstructured N-terminal part (residues 90-124) and a well-defined C-terminal domain (residues 125-228). The C-terminal domain contains three α-helices (residues 144-156, 170-194 and 200-228) and a short antiparallel β-sheet (residues 129-130 and 162-163). Comparison with the structure of the wild-type HuPrP revealed that although two structures share similar global architecture, mutation introduces some local structural differences. The observed variations are mostly clustered in the α₂-α₃ inter-helical interface and in the β₂-α₂ loop region. Introduction of bulkier Ile at position 210 induces reorientations of several residues that are part of hydrophobic core, thus influencing α₂-α₃ inter-helical interactions. Another important structural feature involves the alteration of conformation of the β₂-α₂ loop region and the subsequent exposure of hydrophobic cluster to solvent, which facilitates intermolecular interactions involved in spontaneous generation of PrP^Sc. The NMR structure of V210I mutant offers new clues about the earliest events of the pathogenic conversion process that could be used for the development of antiprion drugs.     

A further study of the bile acids in infants with coprostanic acidemia

The structure of the bile acids in serum of infants with coprostanic acidemia was further investigated. The identity of 3α-hydroxy-5β-cholestan-26-oic acid and 3β-hydroxy-5-cholesten-26-oic acid was confirmed. The biosynthesis of the 3α,7α,12α-trihydroxy-5β-C₂₉ dicarboxylic bile acid does not start from β-sitosterol.     

Crystallization,molecular replacement solution,and refinement of tetrameric β-amylase from sweet potato

Sweet potato β-amylase is a tetramer of identical subunits, which are arranged to exhibit 222 molecular symmetry. Its subunit consists of 498 amino acid residues (Mr 55,880). It has been crystallized at room temperature using polyethylene glycol 1500 as precipitant. The crystals, growing to dimensions of 0.4 mm × 0.4 mm × 1.0 mm within 2 weeks, belong to the tetragonal space group P4₂2₁2 with unit cell dimensions of a = b = 129.63 Å and c = 68.42 Å. The asymmetric unit contains 1 subunit of β-amylase, with a crystal volume per protein mass (V_M) of 2.57 ų/Da and a solvent content of 52% by volume. The three-dimensional structure of the tetrameric β-amylase from sweet potato has been determined by molecular replacement methods using the monomeric structure of soybean enzyme as the starting model. The refined subunit model contains 3,863 nonhydrogen protein atoms (488 amino acid residues) and 319 water oxygen atoms. The current R-value is 20.3% for data in the resolution range of 8–2.3 Å (with 2 σ cut-off) with good stereochemistry. The subunit structure of sweet potato β-amylase (crystallized in the absence of α-cyclodextrin) is very similar to that of soybean β-amylase (complexed with α-cyclodextrin). The root-mean-square (RMS) difference for 487 equivalent Cα atoms of the two β-amylases is 0.96 Å. Each subunit of sweet potato β-amylase is composed of a large (α/β)₈ core domain, a small one made up of three long loops [L3 (residues 91–150), LA (residues 183–258), and L5 (residues 300–327)], and a long C-terminal loop formed by residues 445–493. Conserved Glu 187, believed to play an important role in catalysis, is located at the cleft between the (α/β)₈ barrel core and a small domain made up of three long loops (L3, L4, and L5). Conserved Cys 96, important in the inactivation of enzyme activity by sulfhydryl reagents, is located at the entrance of the (α/β)₈ barrel. © 1995 Wiley-Liss, Inc.     

Cloning, Molecular Characterization, and mRNA Expression of the Thermostable Family 3 β-Glucosidase from the Rare Fungus Stachybotrys microspora

The filamentous fungus Stachybotrys microspora possess a rich β-glucosidase system composed of five β-glucosidases. Three of them were already purified to homogeneity and characterized. In order to isolate the β-glucosidase genes from S. microspora and study their regulation, a PCR strategy using consensus primers was used as a first step. This approach enabled the isolation of three different fragments of family 3 β-glucosidase gene. A representative genomic library was constructed and probed with one amplified fragment gene belonging to family 3 of β-glucosidase. After two rounds of hybridization, seven clones were obtained and the analysis of DNA plasmids leads to the isolation of one clone (CF3) with the largest insert of 7 kb. The regulatory region shows multiple TC-rich elements characteristic of constitutive promoter, explaining the expression of this gene under glucose condition, as shown by zymogram and RT-PCR analysis. The tertiary structure of the deduced amino acid sequence of Smbgl3 was predicted and has shown three conserved domains: an (α/β)₈ triose phosphate isomerase (TIM) barrel, (α/β)₅ sandwich, and fibronectin type III domain involved in protein thermostability. Zymogram analysis highlighted such thermostable character of this novel β-glucosidase.     

Unique assignment of inter-subunit association in GABAA α1β3γ2 receptors determined by molecular modeling

Recent publications defined requirements for inter-subunit contacts in a benzodiazepine-sensitive GABA_A receptor (GABA_ARα1β3γ2). There is strong evidence that the heteropentameric receptor contains two α1, two β3, and one γ2 subunit. However, the available data do not distinguish two possibilities: When viewed clockwise from an extracellular viewpoint the subunits could be arranged in either γ2β3α1β3α1 or γ2α1β3α1β3 configurations. Here we use molecular modeling to thread the relevant GABA_AR subunit sequences onto a template of homopentameric subunits in the crystal structure of the acetylcholine binding protein (AChBP). The GABA_A sequences are known to have 15-18% identity with the acetylcholine binding protein and nearly all residues that are conserved within the nAChR family are present in AChBP. The correctly aligned GABA_A sequences were threaded onto the AChBP template in the γ2β3α1β3α1 or γ2α1β3α1β3  arrangements. Only the γ2α1β3α1β3 arrangement satisfied three known criteria: (1) α1 His¹⁰² binds at the γ2 subunit interface in proximity to γ2 residues Thr¹⁴², Phe⁷⁷, and Met¹³⁰; (2) α1 residues 80-100 bind near γ2 residues 91-104; and (3) α1 residues 58-67 bind near the β3 subunit interface. In addition to predicting the most likely inter-subunit arrangement, the model predicts which residues form the GABA and benzodiazepine binding sites.     

Structural versatility of peptides from Cα, α-disubstituted glycines: Crystal-state conformational analysis of homopeptides from Cα-methyl,Cα-benzylglycine [(αMe)Phe]n

The molecular and crystal structures of one derivative and three homopeptides (from the di-to the tetrapeptide level) of the chiral, C^{α, α}-disubstituted glycine C^α-methyl, C^α-benzylglycine [(αMe)Phe], have been determined by x-ray diffraction. The derivative is mClAc-D -(αMe)Phe-OH, and the peptides are pBrBz-[D -(αMe)Phe]₂-NHMe, pBrBz-[D -(αMe)Phe]₃-OH hemihydrate, and pBrBz-[D -(αMe)Phe]₄-OtBu sesquihydrate. All (αMe)Phe residues prefer ?,ψ torsion angles in the helical region of the conformational map. The dipeptide methylamide and the tripeptide carboxylic acid adopt a β-turn conformation with a 1 ← 4 C?O…?H? N intramolecular H bond. The structure of the tripeptide carboxylic acid is further stabilized by a 1 ← 4 C?O…?H? O intramolecular H bond, forming an “oxy-analogue” of a β-turn. The tetrapeptide ester is folded in a regular (incipient) 3₁₀-helix. In general, the relationship between (αMe)Phe chirality and helix screw sense is opposite to that exhibited by protein amino acids. A comparison is made with the conclusions extracted from published work on homopeptides from other C^α-methylated α-amino acids. © 1993 John Wiley & Sons, Inc.     

Inversion of 310-helix screw sense in a (D-αMe)Leu homotetrapeptide induced by a guest D-(αMe)val residue

The terminally blocked tetrapeptide pBrBz-[D -(αMe)Leu]₂-D -(αMe)Val-D -(αMe)Leu-OtBu is folded in the crystal state in a left-handed 3₁₀-helical structure stabilized by two consecutive 1 ← 4 C?O ?H? N intramolecular H-bonds, as determined by X-ray diffraction analysis. A CD study strongly supports the view that this conformation is also that largely prevailing in MeOH solution. A comparison with the published conformation of pBrBz-[D -(αMe)Leu]₄-OtBu indicates that incorporation of a single internal β-branched (αMe)Val guest residue into the host homo-tetrapeptide from the γ-branched (αMe)Leu residue is responsible for a dramatic structural perturbation, i.e. an inversion of the 3₁₀ screw sense from right to left-handed.     

Structure of Bovine αs-Casein

The secondary structure of bovine α_s-casein and chemically modified α_s-casein in various solvents was investigated by infrared absorption spectrum and optical rotatory dispersion measurements. Amino groups of α_s-casein were either succinylated or acetylated, and carboxyl groups were either methylated or ethylated. Acetylated- and ethylated-α_s-caseins are insoluble in water. Water-soluble samples have unordered structure in water. In organic solvents, such as 2-chloroethanol and ethylene glycol, they have about 50% α-helical fraction. On the other hand, it was found that methylated-α_s-casein had two infrared absorption peaks centered at 1625 and 1643 cm^?1 in D₂O-CH₃OD mixed solvent. This fact may be connected with the presence of β-structure. In the case of solid film of this sample, cast from solution containing CH₃OH, the presence of β-structure was indicated, too. The authors attempted to explain the formation of β-structure in methylated-α_s-casein in terms of the electrostatic interactions due to the differences in the net charge between methylated and unmodified α_s-caseins.     

The role of β1Pix/caveolin-1 interaction in endothelin signaling through Gα subunits

Endothelin-1 (ET-1) is a potent mitogen that transmits signals through its cognate G protein-coupled receptors to stimulate extracellular signal-regulated kinase Erk1/2. Endothelin-1 receptors (ET-Rs) are known to interact with caveolin-1 and co-localize in caveolae which integrate different receptor and signaling proteins. We have recently shown that β₁Pix binds specifically to ET-Rs. Here, we show that β₁Pix binding to caveolin-1 is dependent on heterotrimeric G proteins activation state. β₁Pix interaction with different G proteins is increased in the presence of the G protein activator AMF. Moreover, extraction of cholesterol with methyl-β-cyclodextrin disrupts the binding of β₁Pix to Gα_q, Gα₁₂ and phospho-Erk1/2 but not the binding of β₁Pix to G_β1. The disruption of β₁Pix dimerization strongly reduced the binding of caveolin-1, Gα_q and Gα₁₂. Constitutively active mutants of Gα_q and Gα₁₂ increased Cdc42 activation when co-expressed with β₁Pix but not in the presence of β₁Pix dimerization deficient mutant β₁PixΔ (602-611). ET-1 stimulation increased the binding of phosphorylated Erk1/2 to β₁Pix but not to β₁PixΔ (602-611). RGS3 decreased ET-1-induced Cdc42 activation. These results strongly suggest that the activation of ET-Rs leads to the compartmentalization and the binding of Gα_q to β₁Pix in caveolae, where dimeric β₁Pix acts as platform to facilitate the binding and the activation of Erk1/2.     

Solution structure and mapping of a very weak calcium-binding site of human translationally controlled tumor protein by NMR

Human translationally controlled tumor protein (TCTP) is a growth-related, calcium-binding protein. We determined the solution structure and backbone dynamics of human TCTP, and identified the calcium-binding site of human TCTP using multi-dimensional NMR spectroscopy. The overall structure of human TCTP has a rather rigid well-folded core and a very flexible long loop connected by a short two-strand β-sheet, which shows a conserved fold in the TCTP family. The C-terminal portions of loop L_α3β8 and strand β9 and the N-terminal region of strand β8 may form a calcium-binding site in the human TCTP structure, which is largely conserved in the sequence alignment of TCTPs. The K_d value for the calcium binding is 0.022-0.025 M indicating a very weak calcium-binding site.     

Differential response of two models of genetically modified mice fed with high fat and cholesterol diets: relationship to the study of non-alcoholic steatohepatitis

Thyroid hormone deficiency has been reported to decrease expression and function of both β₁- and β₂-adrenoceptor in different tissues including heart. The purpose of this study was to examine the possible contribution of β₃-adrenoceptors to cardiac dysfunction in hypothyroidism. In addition, effect of this pathology on β₁- and β₂-adrenoceptor was investigated. Hypothyroidism was induced by adding methimazole (300 mg/l) to drinking water of rats for 8 weeks. Cardiac hemodynamic parameters were measured in anesthetised rats in vivo. Responses to β-adrenoceptor agonists were examined in rat papillary muscle in vitro. We also studied the effect of hypotyroidism on mRNA expression of β-adrenoceptors, Giα, GRK, and eNOS in rat heart. All of the hemodynamic parameters (systolic, diastolic and mean arterial pressure, left ventricular pressure, heart rate, +dp/dt, and ?dp/dt) were significantly reduced by the methimazole treatment. The negative inotropic effect elicited by BRL 37344 (a β₃-adrenoceptor preferential agonist) and positive inotropic effects produced by isoprenaline and noradrenaline, respectively, were significantly decreased in papillary muscle of hypothyroid rats as compared to those of controls. On the other hand, hypothyroidism resulted in increased cardiac β₂- and β₃-adrenoceptor, Giα₂, Giα₃, GRK3, and eNOS mRNA expressions. However, β₁-adrenoceptor and GRK2 mRNA expressions were not changed significantly in this pathology. These results show that mRNA expression of β₃-adrenoceptors as well as the signalling pathway components mediated through β₃-adrenoceptors are significantly increased in hypothyroid rat heart. Since we could not correlate these alternates with the decreased negative inotropic response mediated by this receptor subtype, it is not clear whether these changes are important for hypothyroid induced reduction in cardiac function.     

A pentapeptide model for an early folding step in the refolding of staphylococcal nuclease: The role of its turn propensity

Recently the folding of a staphylococcal nuclease (P117G) variant was examined with the hydrogen-deuterium (H-D) exchange technique. Many of the residues that showed significant protection are located in protection are located in β-sheet regions. About half the residues protected belong to an antiparallel β-hairpin structure (residues 21–35) in the native structure. The β-hairpin structure is formed by strands 2 and 3 of sheet 2 connected by the sequence²⁷ Y KGQP³¹ in a type I′ reverse turn conformation with a 4 → 1 hydrogen bonding between Q30 NH and Y27 C=O. We have targeted the conformational characterization of the peptide model Ac-YKGQP-NH₂ with ¹II two-dimensional nmr techniques in aqueous solution with a view to assessing its propensity to sample turn conformational forms and thus initiate the formation of β-hairpin structure. Based upon the observed dαn (i, i + 1), dαn (i, i + 3), and dnn (i, i + 1) nuclear Overhauser effect connectivities, temperature coefficients for amide protons and conformational analysis with quantum mechanical perturbative configuration interaction over localized orbitals method, we conclude that the model peptide samples turn conformational forms with reduced conformational entropy. We suggest that the turn can nucleate the formation of the β-hairpin structure in the refolding of nuclease. Observation of turn propensity for this sequence is consistent with the folding mechanism of the Greek key motif (present in Staphylococcal nuclease) proposed in the literature. © 1997 John Wiley & Sons, Inc.     

Molecular dynamics simulations of the effect of the G-protein and diffusible ligands on the β2-adrenergic receptor

G-protein-coupled receptors have extraordinary therapeutic potential as targets for a broad spectrum of diseases. Understanding their function at the molecular level is therefore essential. A variety of crystal structures have made the investigation of the inactive receptor state possible. Recently released X-ray structures of opsin and the β₂-adrenergic receptor (β₂AR) have provided insight into the active receptor state. In addition, we have contributed to the crystal structure of an irreversible agonist-β₂ adrenoceptor complex. These extensive studies and biophysical investigations have revealed that agonist binding leads to a low-affinity conformation of the active state that is suggested to facilitate G-protein binding. The high-affinity receptor state, which promotes signal transduction, is only formed in the presence of both agonist and G-protein. Despite numerous crystal structures, it is not yet clear how ligands tune receptor dynamics and G-protein binding. We have now used molecular dynamics simulations to elucidate the distinct impact of agonist and inverse agonist on receptor conformation and G-protein binding by investigating the influence of the ligands on the structure and dynamics of a complex composed of β₂AR and the C-terminal end of the Gα_s subunit (GαCT). The simulations clearly showed that the agonist isoprenaline and the inverse agonist carazolol influence the ligand-binding site and the interaction between β₂AR and GαCT differently. Isoprenaline induced an inward motion of helix 5, whereas carazolol blocked the rearrangement of the extracellular part of the receptor. Moreover, in the presence of isoprenaline, β₂AR and GαCT form a stable interaction that is destabilized by carazolol.     

The role of colicin receptors in the uptake of ferrienterochelin by Escherichia coli K-12.

The amino terminal sequences of the 4 caseins synthesized by translation of ovine mammary mRNAs in a wheat germ cell-free system have been investigated by automated Edman degradation. The 3 “calcium-sensitive” caseins (α_s1, α_s2 and β) and κ-casein were synthesized as precaseins with amino terminal hydrophobic extensions of 15 and 21 amino acid residues respectively, resembling “signal peptides” of other secretory proteins. The extra pieces of the 4 caseins, which start with a methionyl residue, end with an alanyl residue which may be one of the signals recognized by the mammary membrane-bound enzyme responsible for the specific cleavage of precaseins. The amino terminal extensions of α_s1, α_s2 and β-caseins show a high degree of homology suggesting that they have derived from a common ancestor.     

Divergent evolution of a β/α-barrel subclass: Detection of numerous phosphate-binding sites by motif search

Study of the most conserved region in many β/α-barrels, the phosphate-binding site, revealed a sequence motif in a few β/α-barrels with known tertiary structure, namely glycolate oxidase (GOX), cytochrome b₂ (Cyb2), tryptophan synthase α subunit (TrpA), and the indoleglycerolphosphate synthase (TrpC). Database searches identified this motif in numerous other enzyme families: (1) IMP dehydrogenase (IMPDH) and GMP reductase (GuaC); (2) phosphoribosylformimino-5-aminoimidazol carboxamide ribotide isomerase (HisA) and the cyclase-producing D-erythro-imidazole-glycerolphosphate (HisF) of the histidine biosynthetic pathway; (3) dihydroorotate dehydrogenase (PyrD); (4) glutamate synthase (GltB); (5) ThiE and ThiG involved in the biosynthesis of thiamine as well as related proteins; (6) an uncharacterized open reading frame from Erwinia herbicola; and (7) a glycerol uptake operon antiterminator regulatory protein (GlpP). Secondary structure predictions of the different families mentioned above revealed an alternating order of β-strands and α-helices in agreement with a β/α-barrel-like topology. The putative phosphate-binding site is always found near the C-terminus of the enzymes, which are all at least about 200 amino acids long. This is compatible with its assumed location between strand 7 and helix 8. The identification of a significant motif in functionally diverse enzymes suggests a divergent evolution of at least a considerable fraction of β/α-barrels. In addition to the known accumulation of β/α-barrels in the tryptophan biosynthetic pathway, we observe clusters of these enzymes in histidine biosynthesis, purine metabolism, and apparently also in thiamine biosynthesis. The substrates are mostly heterocyclic compounds. Although the marginal sequence similarities do not allow a reconstruction of the barrel spreading, they support the idea of pathway evolution by gene duplication.     

Structure of α6β3δ GABAA receptors and their lack of ethanol sensitivity

Delta (δ) subunit containing GABA_A receptors are expressed extra‐synaptically and mediate tonic inhibition. In cerebellar granule cells, they often form a receptor together with α₆ subunits. We were interested to determine the architecture of these receptors. We predefined the subunit arrangement of 24 different GABA_A receptor pentamers by subunit concatenation. These receptors (composed of α₆, β₃ and δ subunits) were expressed in Xenopus oocytes and their electrophysiological properties analyzed. Currents elicited in response to GABA were determined in presence and absence of 3α, 21‐dihydroxy‐5α‐pregnan‐20‐one and to 4,5,6,7‐tetrahydroisoxazolo[5,4‐c]‐pyridin‐3‐ol. α₆‐β₃‐α₆/δ receptors showed a substantial response to GABA alone. Three receptors, β₃‐α₆‐δ/α₆‐β₃, α₆‐β₃‐α₆/β₃‐δ and β₃‐δ‐β₃/α₆‐β₃, were only uncovered in the combined presence of the neurosteroid 3α, 21‐dihydroxy‐5α‐pregnan‐20‐one with GABA. All four receptors were activated by 4,5,6,7‐tetrahydroisoxazolo[5,4‐c]‐pyridin‐3‐ol. None of the functional receptors was modulated by physiological concentrations (up to 30 mM) of ethanol. GABA concentration response curves indicated that the δ subunit can contribute to the formation of an agonist site. We conclude from the investigated receptors that the δ subunit can assume multiple positions in a receptor pentamer composed of α₆, β₃ and δ subunits.     

Comparative studies of asparagine-linked oligosaccharide structures of rat liver microsomal and lysosomal beta-glucuronidases

The sugar chains of microsomal and lysosomal β-glucuronidases of rat liver were studied by endo-β-N-acetylglucosaminidase H digestion and by hydrazinolysis. Only a part of the oligosaccharides released from microsomal β-glucuronidase was an acidic component. The acidic component was not hydrolyzed by sialidase and by calf intestinal and Escherichia coli alkaline phosphatases, but was converted to a neutral component by phosphatase digestion after mild acid treatment indicating the presence of a phosphodiester group. The neutral oligosaccharide portion of microsomal enzyme was a mixture of five high mannose-type sugar chains: (Manα1 → 2)_0~4 [Manα1 → 6(Manα1 → 3)Manα1 → 6(Manα1 → 3)Manβ1 → 4GlcNAcβ1 → 4GlcNAc]. In contrast, lysosomal enzyme contains only Manα1 → 6 (Manα1 → 3) Manα1 → 6(Manα1 → 3) Manβ1 → 4GlcNAcβ1 → 4GlcNAc. The result indicates that removal of α1 → 2-linked mannosyl residues from (Manα1 → 2)₄[Manα1 → 6(Manα1 → 3)Manα1 → 6(Manα1 → 3)Manβ1 → 4GlcNAcβ1 → 4GlcNAc → Asn] starts already in the endoplasmic reticulum of rat liver.     

Synthesis of blockwise alkylated (1→4) linked trisaccharides as surfactants: influence of configuration of anomeric position on their surface activities

New carbohydrate-based surfactants consisting of hydrophilic cellobiosyl and hydrophobic glucosyl residues, methyl β-d-glucopyranosyl-(1→4)-α-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-α-d-glucopyranoside 1 (GβGαMα, G: glucopyranosyl residue, α and β: α-(1→4)- and β-(1→4) glycosidic bonds, M: methyl group), 2 (G_βG_βM_α), 3 (G_βG_αM_β), 4 (G_βG_βM_β), 5 (G_βG_αE_α, E: ethyl group), 6 (G_βG_βE_α), 7 (G_βG_αE_β), 8 (G_βG_βE_β) and eight α-and β-glycoside mixtures (a mixture of 1 and 2: 1/2 = 62/38 (9), 32/68 (10); a mixture of 3 and 4: 3/4 = 69/31 (11), 32/68 (12); a mixture of 5 and 6: 5/6 = 62/38 (13), 33/67 (14); a mixture of 7 and 8: 7/8 = 59/41 (15), 29/71 (16)) were synthesized via combined methods consisting of acid-catalyzed alcoholysis of cellulose ethers and glycosylation of phenyl thio-cellobioside derivatives. Their surface activities in aqueous solution depended on their chemical structures: α- or β-(1→4) linkage between hydrophilic cellobiosyl and hydrophobic glucosyl blocks, methyl or ethyl groups of hydrophobic glucosyl block, and α- or β-linked ether group at the C-1 of hydrophobic glucosyl block. The mixing effect of α- and β-glycosides on surface activities was also investigated. As a result, ethyl β-d-glucopyranosyl-(1→4)-α-d-glucopyranosyl-(1→4)-2,3,6-tri-O-ethyl-β-d-glucopyranoside 7 (G_βG_αE_β) had the highest surface activity, and its critical micellar concentration (CMC) and γ_CMC (surface tension at CMC) values of compound 7 were 0.5 mM (ca. 0.03 wt %) and 34.5 mN/m, respectively. The surface tensions of α- and β-glycoside mixtures except for compounds 9 and 10 were almost equal to those of pure compounds. The syntheses of the mixtures of α- and β-glycosides without purification process are easier than those of pure compounds. Thus, the mixtures should be more practical compounds for industrial use as a surfactant.