Alpha-amylase variants having an elevated solvent stability, method for the production thereof and detergents and cleansers containing these alpha-amylase variants
The present invention relates to α-amylase variants that are stabilized to solvent-exerted hydrolysis, in particular at elevated temperatures or high pH, by point mutagenesis of asparagine (N) or glutamine (Q) residues located on the surface of the molecule to give other amino acid residues. The invention further relates to methods of increasing the stability of an α-amylase to solvent-exerted hydrolysis, in particular at elevated temperatures or high pH, whereby at least one asparagine (N) or glutamine (Q) residue on the surface of the molecule is replaced with a different amino acid residue. The α-amylase variants obtained thereby exhibit better stability to influences of the solvent, increased processivity, and are suited for numerous industrial areas of use, in particular as active ingredients in detergents and cleansers.
1. An isolated α-amylase variant having amylase activity and having at least one amino acid substitution with respect to a predetermined α-amylase starting molecule, wherein in said at least one amino acid substitution an asparagine (N) or a glutamine (Q) residue on the surface of said starting molecule is replaced with A, C, F, G, H, I, K, L, M, P, R, S, T, V, W or Y in the variant, and wherein the starting molecule is an α-amylase having at least 96% sequence identity to positions +1 to 484 of SEQ ID NO: 2 obtained from Bacillus sp. A 7-7 (DSM 12368), said α-amylase variant having improved stability at elevated temperatures or alkaline pH.
2. An α-amylase variant according to claim 1 , wherein in said amino acid substitution N is replaced with A, G, K, R, S or T, or Q is replaced with A, G, I, K, R, S or T.
3. An α-amylase variant according to claim 1 , wherein said asparagine (N) glutamine (Q) residue has an accessibility of at least 10% prior to amino acid substitution, said accessibility of the residue being calculated on a scale from 0% (not accessible to the solvent) to 100% (present in a hypothetical pentapeptide, GGXGG).
4. An α-amylase variant according to claim 1 having from 2 to 10 amino acid substitutions.
5. An α-amylase variant according to claim 1 , wherein the Bacillus sp. A 7-7 (DSM 12368) α-amylase or hybrid amylases therefrom further comprise at least one additional point mutation.
6. An α-amylase variant according to claim 5 , wherein the at least one additional point mutation is selected from the group consisting of the positions: 5, 167, 170, 177, 202, 204, 271, 330, 377, 385 and 445, according to the numbering of the mature protein according to SEQ ID NO. 2.
7. An α-amylase variant according to claim 6 , wherein the at least one additional point mutation is selected from the group consisting of 5A, 167R, 170P, 177L, 202L, 204V, 271D, 330D, 377R, 385S and 445Q.
8. A detergent or cleaning agent comprising an α-amylase variant according to claim 1 .
9. An agent according to claim 8 , comprising from 0.000001 percent by weight to 5% by weight of the α-amylase variant.
10. An agent according to claim 8 , further including at least one additional enzyme selected from the group consisting of amylases, proteases, lipases, cutinases, hemicellulases, cellulases, β-glucanases, oxidases, peroxidases, perhydrolases and laccases.
11. An agent according to claim 8 further comprising at least one additional component, wherein the α-amylase variant is stabilized, and/or its contribution to the washing or cleaning performance of the agent is increased, by the at least one additional component.
12. An agent according to claim 8 , the agent being a solid including at least one compacted component.
13. An agent according to claim 8 , the agent being liquid, gel-like or paste-like, the α-amylase variant being encapsulated.
14. A method of cleaning textiles or hard surfaces, the method comprising:
(a) applying an agent including at least one α-amylase variant according to claim 1 to a textile of hard surface substrate, and
(b) activating the at least one α-amylase variant.
15. A method according to claim 14 , wherein the agent comprises from 0.01 mg to 400 mg of the at least one α-amylase variant.