Characterization of a new cell-bound alpha-amylase in Bacillus subtilis 168 Marburg that is only immunologically related to the exocellular alpha-amylase

A multifunctional α-amylase BSGH13 from Bacillus subtilis BS-5 possessing endoglucanase and xylanase activities

Exploring new multifunctional enzymes and understanding the mechanisms of catalytic promiscuity will be of enormous industrial and academic values. In the present study, we reported the discovery and characterization of a multifunctional enzyme BSGH13 from Bacillus subtilis BS-5. Remarkably, BSGH13 possessed α-amylase, endoglucanase, and xylanase activities. To our knowledge, this was the first report on an amylase from Bacillus species having additional endoglucanase and xylanase activities. Subsequently, we analyzed the effects of aromatic residues substitution at each site of the active site architecture on ligand-binding affinity and catalytic specificity of BSGH13 by a combination of virtual mutation and site-directed mutagenesis approaches. Our results indicated that the introduction of aromatic amino acids Phe or Trp at the positions L182 and L183 altered the local interaction network of BSGH13 towards different substrates, thus changing the multifunctional properties of BSGH13. Moreover, we provided an expanded perspective on studies of multifunctional enzymes.

Molecular characterization of a dimeric intracellular maltogenic amylase of Bacillus subtilis SUH4-2

An additional amylase besides the typical alpha-amylase was detected in the cytoplasm of Bacillus subtilis SUH4-2, an isolate from Korean soil. The corresponding gene encoded a maltogenic amylase, which hydrolyzed cyclodextrin or starch to maltose and glucose; pullulan to panose; acarbose to glucose and acarviosine-glucose. Maltogenic amylase of B. subtilis SUH4-2 transferred sugar molecules to form various branched oligosaccharides upon the hydrolysis of substrates. The enzyme existed in a monomer-dimer equilibrium with a molar ratio of 3:2 in 50 mM KH(2)PO(4)-NaOH buffer (pH 7.0). The maltogenic amylase is most likely to be associated with carbohydrate metabolism in the cytoplasm, since the nucleotide sequence of the gene was highly homologous to the yvdF gene of B. subtilis 168, which is located in a gene cluster involved in maltose/maltodextrin utilization.

Anionic polymers of Bacillus subtilis cell wall modulate the folding rate of secreted proteins

In order to characterize the dynamics of the interaction between the emergent membrane translocated exoprotein and the components of Bacillus subtilis cell wall, we examined the kinetics of the in vitro refolding of levansucrase and alpha-amylase, at pH 7 and 37 degrees C, in the presence of polyphosphates (polyP) of various chain lengths (2</=n</=65). These soluble anionic polymers are considered here to mimic the role of teichoic acids. Even in the absence of calcium, levansucrase rapidly refolded in the presence of polyP of n>/=16. In contrast, polyP modulate indirectly the rate of alpha-amylase refolding via their affinity for calcium. These differential effects might explain that the rate of the cell wall translocation of alpha-amylase secretion was found to be half that of levansucrase.

Characterization of a stable intermediate trapped during reversible refolding of Bacillus subtilis alpha-amylase

Bacillus subtilis exocellular alpha-amylase is reversibly refolded after denaturation by guanidine hydrochloride at pH 7 and 37 degrees C. The unfolding-folding transition monitored by intrinsic fluorescence changes and resistance to proteolysis was resolved into a two-state transition. The first step (t1/2 < 1 s) led from D, the totally unfolded state, to C, a stable partially structured state of the protein. This folding intermediate was devoid of any enzyme activity and partially resistant to protease degradation. Calcium was required for the transition from C to N, the native state. This metal did not remain associated with the native form and could be replaced by barium or strontium, but not by magnesium. We discuss the hypothesis that C, the folding intermediate whose further transformation is under kinetic control, is the competent state involved in the secretion process of alpha-amylase.

Characterization of the rate-limiting step of the secretion of Bacillus subtilis alpha-amylase overproduced during the exponential phase of growth

The Bacillus subtilis alpha-amylase gene, amyE, was expressed under the regulated control of sacR, the levansucrase leader region. The gene fusion including the complete amyE coding sequence with the signal peptide sequence was integrated into the chromosome of a degU32(Hy) strain deleted of the sacB DNA fragment. In this genetic contex, alpha-amylase is produced in the culture supernatant at a high level (2% of total protein) during the exponential phase of growth upon induction by sucrose. Pulse-chase experiments showed that the rate-limiting step (t1/2 = 120 s) of the secretion process is the release of a cell-associated precursor form whose signal peptide has been cleaved. The efficiency of this ultimate step of secretion decreased dramatically in the presence of a metal chelator (EDTA) or when the cells were converted to protoplasts. The hypothesis that this step is tightly coupled with the folding process of alpha-amylase occurring within the cell wall environment was substantiated by in vitro folding studies. The unfolding-folding transition, monitored by the resistance to proteolysis, was achieved within the same time range (t1/2 = 60 s) and required the presence of calcium. This metal requirement could possibly be satisfied in vivo by the integrity of the cell wall. The t1/2 of the alpha-amylase release step is double that of levansucrase, although their folding rates are similar. This perhaps indicates that the passage through the cell wall may depend on parietal properties (e.g. metal ion binding and porosity) and on certain intrinsic properties of the protein (molecular mass and folding properties).