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1.
The conversion from α-helix to β-strand that has been widely observed in so-called chameleon sequences has received considerable attention since such a structural change may induce many amyloidogenic proteins to self-assemble into fibrils thus causing fatal diseases. Here we report a large scale-analysis of the energetics of secondary structural conversions in a collection of chameleon sequences retrieved from the Protein Data Bank. Major energetic contributions to the secondary structural conversion were analyzed by carrying out energy decomposition on a pairwise per-residue basis, i.e., (i,i), (i,i ± 1), (i,i ± 2), (i,i ± 3), (i,i ± 4) and > (i,i ± 4) intra-/inter-residual interactions. While the overall potential energy differences were subtle, individual residue-based interacting energy differences were observed to vary significantly depending on the specific type of secondary structural conversion. The average energy difference between α-helix and β-strand, <ΔE
α→β>, in the chameleon sequences varied significantly in (i,i), (i,i ± 1) and > (i,i ± 4) interactions. The major energetic factors in secondary structure conversions were electrostatic interactions and the polar term for solvation energy. In addition, residue-based average energy differences in α-helix → β-strand conversions were well-correlated to those in α-helix → random coil → β-strand conversions (R
2 = 0.92). Assuming that three secondary structural elements can transform in either direction, this strong correlation indicates that the present energy decomposition method using database structures of chameleon sequences provides a reliable tool for the characterization of secondary structure fluctuations in amino acid sequences. 相似文献
2.
Begoña Gómez-Miranda Alicia Prieto Juan Antonio Leal Oussama Ahrazem Jesús Jiménez-Barbero Manuel Bernabé 《Glycoconjugate journal》2003,20(4):239-246
The alkali extractable and water-soluble cell wall polysaccharides F1SS from Aspergillus wentii and Chaetosartorya chrysella have been studied by methylation analysis, 1D- and 2D-NMR, and MALDI-TOF analysis. Their structures are almost identical,
corresponding to the following repeating unit:
[→ 3)-β-D-Galf-(1 → 5)-β-D-Galf-(1 →]
n
→ mannan core.
The structure of this galactofuranose side chain differs from that found in the pathogenic fungus Aspergillus fumigatus, in other Aspergillii and members of Trichocomaceae:
[→ 5)-β-D-Galf-(1 →]
n
→ mannan core.
The mannan cores have also been investigated, and are constituted by a (1 → 6)-α-mannan backbone, substituted at positions
2 by chains from 1 to 7 residues of (1 → 2) linked α-mannopyranoses. Published in 2004.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Seven analogues of p-nitrophenyl T-antigen [Galβ(1→3)GalNAcα(1→O)PNP] have been synthesized as potential substrates for elucidation of the substrate specificity of endo-α-N-acetylgalactosaminidase. These compounds, which are commercially unavailable, include: GlcNAcβ(1→3){GlcNAcβ(1→6)}GalNAcα(1→O)PNP [core 4 type], GalNAcα(1→3)GalNAcα(1→O)PNP [core 5 type], GlcNAcβ(1→6)GalNAcα(1→O)PNP [core 6 type], GalNAcα(1→6)GalNAcα(1→O)PNP [core 7 type], Galα(1→3)GalNAcα(1→O)PNP [core 8 type], Glcβ(1→3)GalNAcα(1→O)PNP and GalNAcβ(1→3)GalNAcα(1→O)PNP. The assembly of these synthetic probes was accomplished efficiently, based on di-tert-butylsilylene(DTBS)-directed α-galactosylation as a key reaction. 相似文献
4.
Density functional theory (DFT) was used to investigate the Rh(I)-catalyzed intermolecular hydroacylation of vinylsilane with
benzaldehyde. All intermediates and transition states were optimized completely at the B3LYP/6-31G(d,p) level (LANL2DZ(f)
for Rh). Calculations indicated that Rh(I)-catalyzed intermolecular hydroacylation is exergonic, and the total free energy
released is −110 kJ mol−1. Rh(I)-catalyzed intermolecular hydroacylation mainly involves the active catalyst CA2, rhodium–alkene–benzaldehyde complex M1, rhodium–alkene–hydrogen–acyl complex M2, rhodium–alkyl–acyl complex M3, rhodium–alkyl–carbonyl–phenyl complex M4, rhodium–acyl–phenyl complex M5, and rhodium–ketone complex M6. The reaction pathway CA2 + R2 → M1b → T1b → M2b → T2b1 → M3b1 → T4b → M4b → T5b → M5b → T6b → M6b → P2 is the most favorable among all reaction channels of Rh(I)-catalyzed intermolecular hydroacylation. The reductive elimination
reaction is the rate-determining step for this pathway, and the dominant product predicted theoretically is the linear ketone,
which is consistent with Brookhart’s experiments. Solvation has a significant effect, and it greatly decreases the free energies
of all species. The use of the ligand Cp′ (Cp′ = C5Me4CF3) decreased the free energies in general, and in this case the rate-determining step was again the reductive elimination reaction. 相似文献
5.
Bretting H Messer M Bornaghi L Kröger L Mischnick P Thiem J 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(8):601-613
Adult snails synthesize in their albumen glands a polysaccharide which is composed exclusively of D- or D- and L-galactose
(Gal) residues which are interglycosidically linked by 1 → 3 and 1 → 6 bonds. It is the only carbohydrate source for embryos
and freshly hatched snails. Two galactosyltransferases are described in this study which are most likely involved in the biosynthesis
of this polysaccharide. One identified in Helix pomatia acts on oligosaccharides and could be used to synthesize a tetrasaccharide when the branched trisaccharide D-Gal-β-(1 → 3)-[D-Galβ-(1 → 6)]-D-Galβ-1 → OMe
was offered as acceptor. This enzyme, requiring Mg++- and Mn++-ions for activity, introduced a linear β-(1 → 6) linkage at the terminal non-reducing ends and was not detected in Biomphalaria glabrata. The other enzyme, which introduced β-(1 → 6) linkages at subterminal D-Gal residues, thus forming branching points in the
polysaccharide, was found in H. pomatia, Arianta arbustorum and B. glabrata with comparable activities. With the enzyme preparation of H. pomatia, up to four D-Gal residues were introduced into vicinal positions, forming single-membered side chains, if a hexasaccharide
with five linearly β-(1 → 3)-linked D-Gal residues was offered as a acceptor. The multiple-branched structure formed is typical
for snail galactans, making this enzyme a prime candidate for the branching enzyme in galactan synthesis. The enzyme activity
could be solubilized and purified by affinity chromatography. In SDS-polyacrylamide electrophoresis, the Helix- derived eluate displayed two bands (68, 37 kDa) and that of Biomphalaria five bands (68, 63, 17.5; 15; 13 kDa). The purified material showed only 8% of the total activity of the crude extracts,
but it could be shown that a phosphatase present in the crude extract can degrade UDP formed in the transfer reaction and
thus drive the reaction to completion.
Accepted: 23 August 2000 相似文献
6.
S. P. Ermakova E. P. Ivanova I. Yu. Bakunina V. V. Mikhailov T. N. Zvyagintseva 《Microbiology》2012,81(3):367-372
The effect of fucoidan, extractive substances from Fucus evanescens and the Laminaria cichorioides protein (an inhibitor of endo-1→3-β-D-glucanase) on the degradation of F. evanescens thallus and on the growth of bacteria involved in this process was studied. The complex of O-glycosyl hydrolases and the level of their enzymatic activity in bacteria cultivated under various conditions depended significantly on the composition of the growth medium. The highest taxonomic diversity was observed for bacteria isolated from the thallus degraded in the control medium (sea water). These bacteria were characterized by very low levels of activity of the enzymes degrading polysaccharides (fucoidan, laminaran, and pustulan). In the presence of 1→3-β-D-glucanase inhibitors, the taxonomic diversity of the microorganisms degrading F. evanescens thallus was decreased, and the activity of O-glycosyl hydrolases (particularly, of fucoidan hydrolases) was increased. 相似文献
7.
Lipopolysaccharides (LPSs) of two strains Pragia fontium 97U116 and 27480 were isolated and characterized; they were close to those of other representatives of the family Enterobacteriaceae in fatty acid composition and contained, respectively, 3-hydroxytetradecanoic acid as the predominant component (45.8 and 45.1%), tetradecanoic (23.5 and 28.9%), hexadecanoic (12.6 and 7.9%), hexadecenoic (12.6 and 7.9%), and dodecanoic (4.9 and 4.2%) fatty acids. The O-specific polysaccharides consisted of linear penta- and tetrasaccharide repeating units: →2)-α-D-Galf-(1→3)-α-L-Rhap2Ac-(1→4)-α-D-GlcpNAc-(1→2)-α-L-Rhap-(1→3)-β-D-GlcpNAc-(1→ →4)-β-D-ManpNAc3NAcA-(1→2)-α-L-Rhap-(1→3)-β-L-Rhap-(1→4)-α-D-GlcpNAc-(1→ The LPSs of P. fontium 97U116 and 27480 were serologically active and belonged to different serogroups; they were less toxic than those of strain E. coli O55:B5, but more pyrogenic than the Pyrogenal preparation. 相似文献
8.
E. A. Turovsky M. V. Turovskaya A. V. Berezhnov A. V. Tolmacheva N. P. Kaimachnikov L. P. Dolgacheva V. P. Zinchenko E. I. Maevskii V. V. Dynnik 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2012,6(1):35-44
Experiments on cultured mouse adipocytes (9 days in vitro) using fluorescent microscopy have shown that activation of α1- and α2-adrenoceptors by norepinephrine (NE) or α2-adrenoreceptors by L-arginine evokes transient Ca2+ signals, while activation of m3-cholinoreceptors by acetylcholine (ACh) or betaine causes sustained or damped Ca2+ oscillations. The presence in the incubation medium of L-arginine at a low concentration (100–200 μM) is necessary for a vigorous manifestation of these effects, apparently due to
transition of protein kinase G (PKG) and phosphodiesterase V into an active state. In the presence of 1–10 mM L-arginine, the amplitude of the Ca2+ transient response to NE increases and signal duration decreases. ACh and NE upon a sequential addition mutually potentiate
their effects. Using an inhibitory analysis we show that the observed modes are related to the operation of a signaling pathway
with the participation of phosphatidylinositol 3-kinase (PI3K), protein kinase B (PKB), endothelial NO synthase (eNOS), cytoplasmic
guanylate cyclase (sGC), protein kinase G (PKG), ADP-ribosyl cyclase (CD38), and the ryanodine receptor (RyR). The formation
of several loops of positive feedbacks (PF) and negative feedbacks (NF) in the signaling system is possible: (i) short PF
loops due to Ca2+-induced Ca2+ release (CICR) from internal stores through the inositol trisphosphate receptor (IP3R) and RyR participating in the transient signal formation; (ii) long PF loop Ca2+ → eNOS → sGC → PKG → CD38 → RyR → Ca2+, which can provide necessary conditions for calcium oscillations arising from short PF loops (CICR); (iii) several NF loops
based on PKG-mediated inhibition of IP3R and activation of Ca2+-ATPases of sarco(endo)plasmic reticulum and of the plasma membrane providing a shutdown of signaling by the pathway phospholipase
C → IP3R → Ca2+ and limiting Ca2+ rise caused by the pathway PI3K → PKB → eNOS → sGC → PKG → CD38 → RyR → Ca2+. Convergence of signaling pathways that involve α1-, α2-, and m3-receptors and then Gβγ-subunits of Gq and Gq proteins acting on PI3Kγ can provide activation of cytoplasmic PKG, which plays a key role in producing transient responses,
in activation of Ca2+ removal and generation of [Ca2+]i oscillations. PKG inhibition (implemented here by KT5823 application) in the presence of any agonist results in rupture of
NF loops controlling Ca2+ transporting systems activity that leads to uncontrolled [Ca2+]i rise and cell death. 相似文献
9.
Anaerobic biodegradation of triphenylmethane dyes in a hybrid UASFB reactor for wastewater remediation 总被引:1,自引:0,他引:1
Anaerobic digestions have been proved more successful than aerobic systems for the degradation and destruction of dye-containing
wastewaters. The performance of a hybrid up flow anaerobic sludge-filter bed (UASFB) reactor was tested with a synthetic wastewater
containing Crystal violet (CV) as a carbon source and sodium acetate as a co-substrate. Continuous feeding of the reactor
started with an initial OLR of 0.9 g COD/l-d and then it was increased step wise to 4 g COD l−1 d−1, while maintaining constant HRT (24 h). The optimum pH value and temperature for decolorization of crystal violet by this
mixed culture species under anaerobic conditions were found to be 8–9 and 30–35°C respectively. N,N-dimethylaminophenol and N,N-bis (dimethylamino) benzophenone (Michler’s Ketone) were detected as the degradative metabolites of Crystal Violet. Subsequently,
N,N-dimethylaminophenol was further degraded to aniline in the reactor whereas Michler’s ketone was not degraded under anaerobic
conditions. The UASFB bioreactor was able to remove the CV completely up to a loading rate of 100 mg CV l−1d−1. 相似文献
10.
Taekhee Lee Sergey A. Grinshpun Ki Youn Kim Yulia Iossifova Atin Adhikari Tiina Reponen 《Aerobiologia》2006,22(3):227-235
In this exploratory study, indoor and outdoor airborne fungal spores, pollen, and (1→3)-β-D-glucan levels were determined through long-term sampling (24-h) using a Button Personal Inhalable Aerosol Sampler. The air samples were collected in five Cincinnati area homes that had no visible mold growth. The total count of fungal spores and pollen in the collected samples was conducted under the microscope and Limulus Amebocyte Lysate (LAL) chromogenic assay method was utilized for the determination of the (1→3)-β-D-glucan concentration. For the combined number concentration of fungal spores and pollen, the indoor and outdoor geometric mean values were 573 and 6,435 m−3, respectively, with a geometric mean of the Indoor/Outdoor (I/O) ratio of .09. The geometric means of indoor and outdoor (1→3)-β-D-glucan concentrations were .92 and 6.44 ng m−3, respectively, with a geometric mean of the I/O ratio equal to .14. The I/O ratio of (1→3)-β-D-glucan concentration was found to be marginally greater than that calculated based on the combined number concentration of fungal spores and pollen. This suggests that (1→3)-β-D-glucan data are affected not only by intact spores and pollen grains but also by the airborne fragments of fungi, pollen, and plant material, which are ignored by traditional enumeration methodologies. Since the (1→3)-β-D-glucan level may elucidate the total exposure to fungal spores, pollen, and fungal fragments, its I/O ratio may be used as a risk marker for mold and pollen exposure in indoor environments. 相似文献
11.
A. S. Boiko O. N. Smol’kina Yu. P. Fedonenko E. L. Zdorovenko V. V. Kachala S. A. Konnova V. V. Ignatov 《Microbiology》2010,79(2):197-205
Lipopolysaccharides (LPS) and O-specific polysaccharides (OPS) were obtained from the outer membrane of four Azospirillum strains previously assigned to serogroup I based on the serological affinity revealed by the antibodies (AB) to the LPS of
A. brasilense Sp245. Investigation, including determination of monosaccharide composition, methylation analysis, and one- and two-dimensional
NMR spectroscopy, was carried out to determine the OPS structure. The OPSs of A. brasilense Sp107 and S27 and of A. lipoferum RG20a were found to have an identical structure of repeating units represented by a linear penta-D-rhamnan, as was previously
described for the OPSs of A. brasilense Sp245 and SR75. The OPS of A. brasilense SR15 was found to consist of tetrasaccharide repeating units of the following structure: → 2)-α-D-Rhap-(1 → 2)-β-D-Rhap-(1 → 3)-α-D-Rhap-(1 → 2)-α-D-Rhap-(1 →. An opine compound, Nδ-(1-carboxyethyl)-ornithine, closely associated with the LPS of A. brasilense SR15, was identified in azospirilla for the first time. The presence of a 6-deoxisugar (D-rhamnose) in the OPS structure
was shown to be the chemical basis of the serological similarity and the reason for classification of these strains within
the serogroup I. 相似文献
12.
Anja Hemmingsen Anthony A Fryer Michael Hepple Richard C Strange Monica A Spiteri 《Respiratory research》2001,2(4):255-6
Background
The glutathione S-transferase (GST) enzyme GSTP1 utilizes byproducts of oxidative stress. We previously showed that alleles of GSTP1 that encode the Ile105→Val105 substitution are associated with the asthma phenotypes of atopy and bronchial hyperresponsiveness (BHR). However, a further polymorphic site (Ala114→Val114) has been identified that results in the following alleles: GSTP1 * A (wild-type Ile105→Ala114), GSTP1 * B (Val105→Ala114), GSTP1 * C (Val105→Val114) and GSTP1 * D (Ile105→Val114). 相似文献13.
A. V. Perepelov Bin Liu S. N. Senchenkova A. S. Shashkov S. D. Shevelev Lu Feng Lei Wang Y. A. Knirel 《Biochemistry. Biokhimii?a》2010,75(1):19-24
On mild acid degradation of the lipopolysaccharide of Escherichia coli O108, the O-polysaccharide was isolated and studied by sugar analysis and one- and two-dimensional 1H- and 13C-NMR spectroscopy. The polysaccharide was found to contain an unusual higher sugar, 5,7-diacetamido-3,5,7,9-tetradeoxy-l-glycero-d-galacto-non-2-ulosonic acid (di-N-acetyl-8-epilegionaminic acid, 8eLeg5Ac7Ac). The following structure of the tetrasaccharide repeating unit of the polysac-charide
was established: →4)-α-8eLegp5Ac7Ac-(2→6)-α-D-Galp-(1→3)-α-L-FucpNAc-(1→3)-α-D-GlcpNAc-(1→. Functions of the E. coli O108 antigen biosynthetic genes, including seven putative genes for synthesis of 8eLeg5Ac7Ac, were assigned by sequencing
the O-antigen gene cluster along with comparison with gene databases and known biosynthetic pathways for related nonulosonic
acids. 相似文献
14.
M. I. Kusaykin A. O. Chizhov A. A. Grachev S. A. Alekseeva I. Yu Bakunina O. I. Nedashkovskaya V. V. Sova T. N. Zvyagintseva 《Journal of applied phycology》2006,18(3-5):369-373
Specificities of actions of fucoidanases from the marine microorganism Pseudoalteromonas citrea KMM 3296 and the marine mollusk Littorina kurila were studied. The enzymes possess similar specificities and catalyze the cleavage of accessible α-(1→3)-fucoside bonds in fucoidans with highly sulfated α-(1→4; 1→3)-L-fucooligosaccharides. A high degree of sulfation of the fucose residues in fucoidans makes α-(1→3)-L-fucoside bonds inaccessible for the action of the studied enzymes. The maximum degree of cleavage of fucoidan was achieved by the fucoidanase from the marine bacterium Pseudoalteromonas citrea KMM 3296. 相似文献
15.
AM Zakharenko MI Kusaykin SN Kovalchuk VV Sova AS Silchenko AA Belik SD Anastyuk BM Ly VA Rasskazov TN Zvyagintseva 《Biochemistry. Biokhimii?a》2012,77(8):878-888
A specific 1→3-β-D-glucanase with molecular mass 37 kDa was isolated in homogeneous state from crystalline style of the commercial marine mollusk Tapes literata. It exhibits maximal activity within the pH range from 4.5 to 7.5 at 45dgC. The 1→3-β-D-glucanase catalyzes hydrolysis of β-1→3 bonds in glucans as an endoenzyme with retention of bond configuration, and it has transglycosylating activity. The K m for hydrolysis of laminaran is 0.25 mg/ml. The enzyme is classified as a glucan endo-(1→3)-β-D-glucosidase (EC 3.2.1.39). The cDNA encoding this 1→3-β-D-glucanase from T. literata was sequenced, and the amino acid sequence of the enzyme was determined. The endo-1→3-β-D-glucanase from T. literata was assigned to the 16th structural family (GHF 16) of O-glycoside hydrolases. 相似文献
16.
Van Laere KM Hartemink R Beldman G Pitson S Dijkema C Schols HA Voragen AG 《Applied microbiology and biotechnology》1999,52(5):681-688
Bifidobacterium adolescentis, a gram-positive saccharolytic bacterium found in the human colon, can, alongside other bacteria, utilise stachyose in vitro
thanks to the production of an α-galactosidase. The enzyme was purified from the cell-free extract of Bi. adolescentis DSM 20083T. It was found to act with retention of configuration (α→α), releasing α-galactose from p-nitrophenyl galactoside. This hydrolysis probably operates with a double-displacement mechanism, and is consistent with the
observed glycosyltransferase activity. As α-galactosides are interesting substrates for bifidobacteria, we focused on the
production of new types of α-galactosides using the transgalactosylation activity of Bi. adolescentisα-galactosides. Starting from melibiose, raffinose and stachyose oligosaccharides could be formed. The transferase activity
was highest at pH 7 and 40 °C. Starting from 300 mM melibiose a maximum yield of 33% oligosaccharides was obtained. The oligosaccharides
formed from melibiose were purified by size-exclusion chromatography and their structure was elucidated by NMR spectroscopy
in combination with enzymatic degradation and sugar linkage analysis. The trisaccharide α-d-Galp-(1 → 6)-α-d-Galp-(1 → 6)-d-Glcp and tetrasaccharide α-d-Galp-(1 → 6)-α-d-Galp-(1 → 6)-α-d-Galp-(1 → 6)-d-Glcp were identified, and this indicates that the transgalactosylation to melibiose occurred selectively at the C-6 hydroxyl group
of the galactosyl residue. The trisaccaride α-d-Galp-(1 → 6)-α-d-Galp-(1 → 6)-d-Glcp formed could be utilised by various intestinal bacteria, including various bifidobacteria, and might be an interesting pre-
and synbiotic substrate.
Received: 15 March 1999 / Received revision: 8 June 1999 / Accepted: 11 June 1999 相似文献
17.
Vimaleswaran KS Radha V Ramya K Babu HN Savitha N Roopa V Monalisa D Deepa R Ghosh S Majumder PP Rao MR Mohan V 《Human genetics》2008,123(6):599-605
Adiponectin is an adipose tissue specific protein that is decreased in subjects with obesity and type 2 diabetes. The objective
of the present study was to examine whether variants in the regulatory regions of the adiponectin gene contribute to type
2 diabetes in Asian Indians. The study comprised of 2,000 normal glucose tolerant (NGT) and 2,000 type 2 diabetic, unrelated
subjects randomly selected from the Chennai Urban Rural Epidemiology Study (CURES), in southern India. Fasting serum adiponectin
levels were measured by radioimmunoassay. We identified two proximal promoter SNPs (−11377C→G and −11282T→C), one intronic
SNP (+10211T→G) and one exonic SNP (+45T→G) by SSCP and direct sequencing in a pilot study (n = 500). The +10211T→G SNP alone was genotyped using PCR-RFLP in 4,000 study subjects. Logistic regression analysis revealed
that subjects with TG genotype of +10211T→G had significantly higher risk for diabetes compared to TT genotype [Odds ratio
1.28; 95% Confidence Interval (CI) 1.07–1.54; P = 0.008]. However, no association with diabetes was observed with GG genotype (P = 0.22). Stratification of the study subjects based on BMI showed that the odds ratio for obesity for the TG genotype was
1.53 (95%CI 1.3–1.8; P < 10−7) and that for GG genotype, 2.10 (95% CI 1.3–3.3; P = 0.002). Among NGT subjects, the mean serum adiponectin levels were significantly lower among the GG (P = 0.007) and TG (P = 0.001) genotypes compared to TT genotype. Among Asian Indians there is an association of +10211T→G polymorphism in the
first intron of the adiponectin gene with type 2 diabetes, obesity and hypoadiponectinemia. 相似文献
18.
Tohru Kobayashi Yasushi Kageyama Nobuyuki Sumitomo Katsuhisa Saeki Tsuyoshi Shirai Susumu Ito 《World journal of microbiology & biotechnology》2005,21(6-7):961-967
Summary Crystallographic analysis of the highly alkaline M-protease from an alkaliphilic Bacillus strain shows the occurrence of a unique salt bridge triad Arg19–Glu271–Arg275 (in subtilisin BPN′ numbering), which is not
found in less alkaline true subtilisins BPN′ and Carlsberg from Bacillus amyloliquefaciens and Bacillus licheniformis, respectively. Because the corresponding residues are all Gln residue in the subtilisin BPN′, Gln residue was engineered
into the position(s) 19, 271 and/or 275 in M-protease by site-directed mutagenesis. Disruptions of the salt bridge caused
the reduction of the thermostability of the mutant proteins at alkaline pH with the following decreasing order of thermal
inactivation rate; the wild-type > Arg275 → Gln > Glu271 → Gln > Arg19 → Gln/Glu271 → Gln/Arg275 → Gln > Arg19 → Gln. This
result provides the evidence that the salt bridge triad contributes to the thermostability and structural rigidity of the
highly alkaline M-protease. 相似文献
19.
Walter Pretsch Bimal Chatterjee Jack Favor Siegbert Merkle Rodica Sandulache 《Mammalian genome》1998,9(2):144-149
Four independent heterozygous lactate dehydrogenase (LDH) mutations with approximately 60% of wild-type enzyme activity in
whole blood have been recovered. The mutant line Ldh1
a2Neu proved to be homozygous lethal, whereas for the three lines Ldh1
a7Neu, Ldh1
a11Neu, and Ldh1
a12Neu homozygous mutants with about 20% residual activity occurred in the progeny of heterozygous inter se matings. However, the
number of homozygous mutants was less than expected, suggesting an increased lethality of these animals. Various physicochemical
and kinetic properties of LDH are altered. Exons of the Ldh1 gene were PCR amplified and sequenced to determine the molecular lesion in the mutant alleles. Ldh1
a2Neu carried an A/T → G/C transition in codon 112 (in exon 3), resulting in an Asn → Asp substitution; Asn112 is part of the helix
αD, which is involved in the coenzyme-binding domain. Ldh1
a7Neu contained an A/T → C/G transversion within the codon for residue 194 in exon 4, causing an Asp → Ala substitution, which
may affect the arrangement of the substrate-binding site. Three base substituions were discovered for the mutation Ldh1
a11Neu in exon 7: the transition C/G → T/A, a silent mutation, and two transversions C/G → A/T and C/G → G/C, both missense mutations,
which led to the amino acid replacements Ala319 → Glu and Thr321 → Ser, respectively, located in the αH helix structure of
the COOH tail of LDHA. We suggest that the mutation is the result of a gene conversion event between Ldh1
a wild-type gene and the pseudogene Ldh1-ps. The alteration Ile → Thr of codon 241 in exon 6 caused by the base pair change T/A → C/G was identified in the mutation
Ldh1
a12Neu; IIe241 is included in the helix α2G, a structure that is indirectly involved in coenzyme binding. Each of the sequence alterations
has a potential impact on the structure of the LDHA protein, which is consistent with the decreased LDH activity and biochemical
and physiological alterations.
Received: 3 July 1997 / Accepted: 30 September 1997 相似文献
20.
The structural investigation of an extracellular polysaccharide released during photoautotrophic growth by the cyanobacterium
Nostoc insulare is reported. After 60 days of cultivation, an average yield of purified, desalted, and freeze-dried released polysaccharide
(RPS) of 0.9 g L−1 medium was obtained. The apparent hydrodynamic volume, determined for RPS, was 1.1 × 106 Da, and the average molecular weight was 2.8 × 106 Da. No sulfate and only traces of pyruvate and acetate groups were detectable. A protein content of only 0.7% indicates a
high degree of purity of RPS. The following constituent uronic acids and sugars were identified: glucuronic acid (GlcA), glucose
(Glc), arabinose (Ara), and for the first time, cyanobacterial RPSs 3-O-methyl-arabinose (3-O-Methyl-Ara). Adapted from linkage
analyses of untreated RPS and of RPS treated by means of reduction of uronic acids, mild acid hydrolysis with oxalic acid,
or lithium degradation, respectively, the following partial structure of RPS is proposed, which possesses an arborisation
built by 1,3,4-Glcp and a side chain built by 3-O-Methyl-Araf: →1)-Glcp-(3→1)-Glcp-[(3→1)-3-O-Methyl-Araf](4→1)-GlcAp-(4→). 相似文献