Isolation of α-amylase on crosslinked starch

Adsorptive Properties of the Preparation Material from the Skin of Corn Stalk for Enzyme Immobilization

In order to investigate the characterizations of skin adsorption material (SAD) prepared from skin of corn stalks by High Boiling Solvent treatment, neutral proteinase and maltogenic amylase were selected as adsorbate to assess its potential applicability for enzyme immobilization. The structure of SAD and Skin were compared by FT-IR and XRD. The characterizations of the adsorption of the different enzymes onto SAD were studied. The isotherm of the maltogenic amylase was found to be linear with the Freundlich equation, and proteinase was found to be linear with the Langmuir equation in the studied concentration range. SAD could be applied the bio-active material and Skin to prepare SAD.

Phage display selects for amylases with improved low pH starch-binding

Directed evolution of secreted industrial enzymes is hampered by the lack of powerful selection techniques. We have explored surface display to select for enzyme variants with improved binding performance on complex polymeric substrates. By a combination of saturation mutagenesis and phage display we selected alpha-amylase variants, which have the ability to bind starch substrate at industrially preferred low pH conditions. First we displayed active alpha-amylase on the surface of phage fd. Secondly we developed a selection system that is based on the ability of alpha-amylase displaying phages to bind to cross-linked starch. This system was used to probe the involvement of specific beta-strands in substrate interaction. Finally, a saturated library of alpha-amylase mutants with one or more amino acid residues changed in their Cbeta4 starch-binding domain was subjected to phage display selection. Mutant molecules with good starch-binding and hydrolytic capacity could be isolated from the phage library by repeated binding and elution of phage particles at lowered pH value. Apart from the wild type alpha-amylase a specific subset of variants, with only changes in three out of the seven possible positions, was selected. All selected variants could hydrolyse starch and heptamaltose at low pH. Interestingly, variants were found with a starch hydrolysis ratio at pH 4.5/7.5 that is improved relative to the wild type alpha-amylase. These data demonstrate that useful alpha-amylase mutants can be selected via surface display on the basis of their binding properties to starch at lowered pH values.