- Molecular insight into regioselectivity of transfructosylation catalyzed by GH68 levansucrase and β-fructofuranosidase
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Glycoside hydrolase family 68 (GH68) enzymes catalyze β-fructosyltransfer from sucrose to another sucrose, the so-called transfructosylation. Although regioselectivity of transfructosylation is divergent in GH68 enzymes, there is insufficient information available on the structural factor(s) involved in the selectivity. Here, we found two GH68 enzymes, β-fructofuranosidase (FFZm) and levansucrase (LSZm), encoded tandemly in the genome of Zymomonas mobilis, displayed different selectivity: FFZm catalyzed the β-(2→1)-transfructosylation (1-TF), whereas LSZm did both of 1-TF and β-(2→6)-transfructosylation (6-TF). We identified His79FFZm and Ala343FFZm and their corresponding Asn84LSZm and Ser345LSZm respectively as the structural factors for those regioselectivities. LSZm with the respective substitution of FFZm-type His and Ala for its Asn84LSZm and Ser345LSZm (N84H/S345A-LSZm) lost 6-TF and enhanced 1-TF. Conversely, the LSZm-type replacement of His79FFZm and Ala343FFZm in FFZm (H79N/A343SFFZm) almost lost 1-TF and acquired 6-TF. H79N/A343S-FFZm exhibited the selectivity like LSZm but did not produce the β-(2→6)-fructoside-linked levan and/or long levanooligosaccharides that LSZm did. We assumed Phe189LSZm to be a responsible residue for the elongation of levan chain in LSZm and mutated the corresponding Leu187FFZm in FFZm to Phe. An H79N/L187F/A343S-FFZm produced a higher quantity of long levanooligosaccharides than H79N/A343S-FFZm (or H79NFFZm), although without levan formation, suggesting that LSZm has another structural factor for levan production. We also found that FFZm generated a sucrose analog, β-D-fructofuranosyl α-D-mannopyranoside, by β-fructosyltransfer to D-mannose and regarded His79FFZm and Ala343FFZm as key residues for this acceptor specificity. In summary, this study provides insight into the structural factors of regioselectivity and acceptor specificity in transfructosylation of GH68 enzymes.
- Kikuchi, Asako,Kimura, Atsuo,Lang, Weeranuch,Okuyama, Masayuki,Sadahiro, Juri,Serizawa, Ryo,Tagami, Takayoshi,Tanuma, Masanari
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- Optimization of levansucrase/endo-inulinase bi-enzymatic system for the production of fructooligosaccharides and oligolevans from sucrose
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A bi-enzymatic system based on the combined use of levansucrase (LS) from Bacillus amyloliquefaciens and endo-inulinase from Aspergillus niger in a one-step reaction was investigated for the synthesis of fructooligosaccharides (FOSs) and oligolevans using sucrose as the sole substrate. Sucrose concentration was the most important independent variable, whilst LS to endo-inulinase ratio exhibited significant effects on the end-product profiles. The interaction between sucrose concentration and reaction time exhibited significant effect on all responses. At the initial stage of time course, short chain FOSs (scFOSs, 1-kestose, nystose, 1F-fructosylnystose) were the major products, whilst 6-kestose, medium chain fructooligosaccharides (mcFOSs, levanohexaose, levanopentaose) and oligolevans became the dominant ones at the late stage. The optimal conditions leading to a high yield of scFOSs (1:1 ratio, 0.5 h, 0.6 M) were different from those resulting in a high yield of mcFOSs and oligolevans (1.85:1 ratio, 1.77 h, 0.6 M). The bi-enzymatic system has a great potential for the production of FOSs and oligolevans at a large scale because of its high yield (57-65%, w/w) and productivity (65.8-266.8 g/L h), and its uses of low temperature (35 °C) and low concentration of sucrose. To the best of our knowledge, this is the first study on the optimization of a LS/endo-inulinase bi-enzymatic system.
- Tian, Feng,Khodadadi, Maryam,Karboune, Salwa
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- Structural and kinetic insights reveal that the amino acid pair Gln-228/Asn-254 modulates the transfructosylating specificity of Schwanniomyces occidentalis β-fructofuranosidase, an enzyme that produces prebiotics
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Schwanniomyces occidentalis β-fructofuranosidase (Ffase) is a GH32 dimeric enzyme that releases fructose from the nonreducing end of various oligosaccharides and essential storage fructans such as inulin. It also catalyzes the transfer of a fructosyl unit to an acceptor producing 6-kestose and 1-kestose, prebiotics that stimulate the growth of bacteria beneficial for human health. We report here the crystal structure of inactivated Ffase complexed with fructosylnystose and inulin, which shows the intricate net of interactions keeping the substrate tightly bound at the active site. Up to five subsites were observed, the sugar unit located at subsite +3 being recognized by interaction with the β-sandwich domain of the adjacent sub-unit within the dimer. This explains the high activity observed against long substrates, giving the first experimental evidence of the direct role of a GH32 β-sandwich domain in substrate binding. Crucial residues were mutated and their hydrolase/transferase (H/T) activities were fully characterized, showing the involvement of the Gln-228/Asn-254 pair in modulating the H/T ratio and the type β(2-1)/β(2-6) linkage formation. We generated Ffase mutants with new transferase activity; among them, Q228V gives almost specifically 6-kestose, whereas N254T produces a broader spectrum product including also neokestose. A model for the mechanism of the Ffase transfructosylation reaction is proposed. The results contribute to an understanding of the molecular basis regulating specificity among GH-J clan members, which represent an interesting target for rational design of enzymes, showing redesigned activities to produce tailor-made fructooligosaccharides.
- Alvaro-Benito, Miguel,Sainz-Polo, M. Angela,Gonzalez-Perez, David,Gonzalez, Beatriz,Plou, Francisco J.,Fernandez-Lobato, Maria,Sanz-Aparicio, Julia
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experimental part
p. 19674 - 19686
(2012/08/14)
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- NMR structural study of fructans produced by Bacillus sp. 3B6, bacterium isolated in cloud water
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Bacillus sp. 3B6, bacterium isolated from cloud water, was incubated on sucrose for exopolysaccharide production. Dialysis of the obtained mixture (MWCO 500) afforded dialyzate (DIM) and retentate (RIM). Both were separated by size exclusion chromatography. RIM afforded eight fractions: levan exopolysaccharide (EPS), fructooligosaccharides (FOSs) of levan and inulin types with different degrees of polymerization (dp 2-7) and monosaccharides fructose:glucose = 9:1. Levan was composed of two components with molecular mass ~3500 and ~100 kDa in the ratio 2.3:1. Disaccharide fraction contained difructose anhydride DFA IV. 1-Kestose, 6-kestose, and neokestose were identified as trisaccharides in the ratio 2:1:3. Fractions with dp 4-7 were mixtures of FOSs of levan (2,6-βFruf) and inulin (1,2-βFruf) type. DIM separation afforded two dominant fractions: monosaccharides with fructose: glucose ratio 1:3; disaccharide fraction contained sucrose only. DIM trisaccharide fraction contained 1-kestose, 6-kestose, and neokestose in the ratio1.5:1:2, penta and hexasaccharide fractions contained FOSs of levan type (2,6-βFruf) containing α-glucose. In the pentasaccharide fraction also the presence of a homopentasaccharide composed of 2,6-linked βFruf units only was identified. Nystose, inulin (1,2-βFruf) type, was identified as DIM tetrasaccharide. Identification of levan 2,6-βFruf and inulin 1,2-βFruf type oligosaccharides in the incubation medium suggests both levansucrase and inulosucrase enzymes activity in Bacillus sp. 3B6.
- Matulová, Mária,Husárová, Slavomíra,Capek, Peter,Sancelme, Martine,Delort, Anne-Marie
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experimental part
p. 501 - 507
(2011/04/22)
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- Formation of trisaccharides (kestoses) by pyrolysis of sucrose
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Amorphous sucrose, containing citric acid as catalyst, undergoes thermolysis at 100° to yield fructofuranosyl cation and D-glucose. The cation reacts with unchanged sucrose to form all three of the known kestoses, and also their α-fructofuranosyl anomers. Two of the latter are resistant to invertase hydrolysis. A new fructosylglucose disaccharide is also formed. Amorphous sucrose, containing citric acid as catalyst, undergoes thermolysis at 100° to yield fructofuranosyl cation and D-glucose. The cation reacts with unchanged sucrose to form all three of the known kestoses, and also their α-fructofuranosyl anomers. Two of the latter are resistant to invertase hydrolysis. A new fructosylglucose disaccharide is also formed.
- Manley-Harris,Richards
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p. 101 - 113
(2007/10/02)
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