A functional raw starch-binding domain of barley alpha-amylase expressed in Escherichia coli

Probing the role of aromatic residues at the secondary saccharide-binding sites of human salivary alpha-amylase in substrate hydrolysis and bacterial binding

Human salivary alpha-amylase (HSAmy) has three distinct functions relevant to oral health: (1) hydrolysis of starch, (2) binding to hydroxyapatite (HA), and (3) binding to bacteria (e.g., viridans streptococci). Although the active site of HSAmy for starch hydrolysis is well-characterized, the regions responsible for bacterial binding are yet to be defined. Since HSAmy possesses several secondary saccharide-binding sites in which aromatic residues are prominently located, we hypothesized that one or more of the secondary saccharide-binding sites harboring the aromatic residues may play an important role in bacterial binding. To test this hypothesis, the aromatic residues at five secondary binding sites were mutated to alanine to generate six mutants representing either single (W203A, Y276A, and W284A), double (Y276A/W284A and W316A/W388A), or multiple [W134A/W203A/Y276A/W284A/W316A/W388A; human salivary alpha-amylase aromatic residue multiple mutant (HSAmy-ar)] mutations. The crystal structure of HSAmy-ar as an acarbose complex was determined at a resolution of 1.5 A and compared with the existing wild-type acarbose complex. The wild-type and the mutant enzymes were characterized for their abilities to exhibit enzyme activity, starch-binding activity, HA-binding activity, and bacterial binding activity. Our results clearly showed that (1) mutation of aromatic residues does not alter the overall conformation of the molecule; (2) single or double mutants showed either moderate or minimal changes in both starch-binding activity and bacterial binding activity, whereas HSAmy-ar showed significant reduction in these activities; (3) starch-hydrolytic activity was reduced by 10-fold in HSAmy-ar; (4) oligosaccharide-hydrolytic activity was reduced in all mutants, but the action pattern was similar to that of the wild-type enzyme; and (5) HA binding was unaffected in HSAmy-ar. These results clearly show that the aromatic residues at the secondary saccharide-binding sites in HSAmy play a critical role in bacterial binding and in starch-hydrolytic functions of HSAmy.

The crystal water affect in the interaction between the tenebrio molitor alpha-amylase and its inhibitor

Molecular dynamics simulation of the interaction between the Tenebrio molitor alpha-amylase and its inhibitor at different proportion of crystal water was carried out with OPLS force field by hyperchem 7.5 software. In the correlative study, the optimal temperature of wheat monomeric and dimeric protein inhibitors was from 273 K to 318 K. The the average temperature of experimentation is 289 K. (1) The optimal temperature of interaction between alpha-amylase and its inhibitors was 280 K without crystal water that was close to the results of experimentation. The forming of enzyme-water and inhibitor-water was easy, but incorporating third monomer was impossible. (2) Having analyzed the potential energy data, the optimal temperature of interaction energy between alpha-amylase and its inhibitors covering 9 : 1, 5 : 5, 4 : 6, and 1 : 9 proportion crystal water was 290 K. (3) We compared the correlative QSAR properties. The proportion of crystal water was close to the data of polarizability (12.4%) in the QSAR properties. The optimal temperature was 280 K. This result was close to 289 K. These findings have theoretical and practical implications.

Synergistic Action of Recombinant α-Amylase and Glucoamylase on the Hydrolysis of Starch Granules

Barley alpha-amylase 1 mutant (AMY) and Lentinula edodes glucoamylase (GLA) were cloned and expressed in Saccharomyces cerevisiae. The purified recombinant AMY hydrolyzed corn and wheat starch granules, respectively, at rates 1.7 and 2.5 times that of GLA under the same reaction conditions. AMY and GLA synergistically enhanced the rate of hydrolysis by approximately 3x for corn and wheat starch granules, compared to the sum of the individual activities. The exo-endo synergism did not change by varying the ratio of the two enzymes when the total concentration was kept constant. A yield of 4% conversion was obtained after 25 min 37 degrees C incubation (1 unit total enzyme, 15 mg raw starch granules, pH 5.3). The temperature stability of the enzyme mixtures was < or =50 degrees C, but the initial rate of hydrolysis continued to increase with higher temperatures. Ca(++) enhanced the stability of the free enzymes at 50 degrees C incubation. Inhibition was observed with the addition of 10 mM Fe(++) or Cu(++), while Mg(++ )and EDTA had lesser effect.

Direct production of ethanol from raw corn starch via fermentation by use of a novel surface-engineered yeast strain codisplaying glucoamylase and alpha-amylase

Direct and efficient production of ethanol by fermentation from raw corn starch was achieved by using the yeast Saccharomyces cerevisiae codisplaying Rhizopus oryzae glucoamylase and Streptococcus bovis alpha-amylase by using the C-terminal-half region of alpha-agglutinin and the flocculation functional domain of Flo1p as the respective anchor proteins. In 72-h fermentation, this strain produced 61.8 g of ethanol/liter, with 86.5% of theoretical yield from raw corn starch.

Engineering a bifunctional starch–cellulose cross-bridge protein

Biodegradable starch- and cellulose-based polymers have a range of properties which make them suitable for use in a wide array of biomedical applications ranging from bone replacement to engineering of tissue scaffolds and drug delivery systems. A novel polysaccharide cross-bridging protein was designed which was comprised of a cellulose-binding domain from Clostridium cellulovorans (CBD(clos)) and a starch-binding domain from Aspergillus niger B1 (SBD(Asp)). The two genes were fused in-frame via a synthetic elastin gene to construct a Cellulose/Starch Cross bridging Protein (CSCP). Recombinant CSCP was expressed in Escherichia coli, and successfully refolded from inclusion bodies. CSCP demonstrated cross-bridging ability in different model systems composed of insoluble or soluble starch and cellulose. The aspect that different carbohydrate-binding module maintain their binding capacity over a wide range of conditions, without the need for chemical reactions, makes them attractive domains for designing new classes of chimeric polysaccharide-binding domains which demonstrate potential for use in a wide range of biomaterials.

Molecular cloning and 3D structure prediction of the first raw-starch-degrading glucoamylase without a separate starch-binding domain

Raw-starch-degrading glucoamylases have been known as multidomain enzymes consisting of a catalytic domain connected to a starch-binding domain (SBD) by an O-glycosylated linker region. A molecular genetics approach has been chosen to find structural differences between two related glucoamylases, raw-starch-degrading Glm and nondegrading Glu, from the yeasts Saccharomycopsis fibuligera IFO 0111 and HUT 7212, respectively. We have found that Glm and Glu show a high primary (77%) and tertiary structure similarity. Glm, although possessing a good ability for raw starch degradation, did not show consensus amino acid residues to any SBD found in glucoamylases or other amylolytic enzymes. Raw starch binding and digestion by Glm must thus depend on the existence of a site(s) lying within the intact protein which lacks a separate SBD. The enzyme represents a structurally new type of raw-starch-degrading glucoamylase.

Cyclomaltodextrinase, neopullulanase, and maltogenic amylase are nearly indistinguishable from each other

Over 20 enzymes denoted as cyclomaltodextrinase, maltogenic amylase, or neopullulanase that share 40-86% sequence identity with each other are found in public data bases. These enzymes are distinguished from typical alpha-amylases by containing a novel N-terminal domain and exhibiting preferential substrate specificities for cyclomaltodextrins (CDs) over starch. In this research field, a great deal of confusion exists regarding the features distinguishing the three groups of enzymes from one another. Although a different enzyme code has been assigned to each of the three different enzyme names, even a single differentiating enzymatic property has not been documented in the literature. On the other hand, an outstanding question related to this issue concerns the structural basis for the preference of these enzymes for CDs. To clarify the confusion and to address this question, we have determined the structures of two enzymes, one from alkalophilic Bacillus sp. I-5 and named cyclomaltodextrinase and the other from a Thermus species and named maltogenic amylase. The structure of the Bacillus enzyme reveals a dodecameric assembly composed of six copies of the dimer, which is the structural and functional unit of the Thermus enzyme and an enzyme named neopullulanase. The structure of the Thermus enzyme in complex with beta-CD led to the conclusion that Trp47, a well conserved N-terminal domain residue, contributes greatly to the preference for beta-CD. The common dimer formation through the novel N-terminal domain, which contributes to the preference for CDs by lining the active-site cavity, convincingly indicates that the three groups of enzymes are not different enough to preserve the different names and enzyme codes.