title: Combinatorial engineering to enhance thermostability of amylosucrase.
abstract: Amylosucrase is a transglucosidase that catalyzes amylose-like polymer synthesis from sucrose substrate. About 60,000 amylosucrase variants from two libraries generated by the MutaGen random mutagenesis method were submitted to an in vivo selection procedure leading to the isolation of more than 7000 active variants. These clones were then screened for increased thermostability using an automated screening process. This experiment yielded three improved variants (two double mutants and one single mutant) showing 3.5- to 10-fold increased half-lives at 50 degrees C compared to the wild-type enzyme. Structural analysis revealed that the main differences between wild-type amylosucrase and the most improved variant (R20C/A451T) might reside in the reorganization of salt bridges involving the surface residue R20 and the introduction of a hydrogen-bonding interaction between T451 of the B' domain and D488 of flexible loop 8. This double mutant is the most thermostable amylosucrase known to date and the only one usable at 50 degrees C. At this temperature, amylose synthesis by this variant using high sucrose concentration (600 mM) led to the production of amylose chains twice as long as those obtained by the wild-type enzyme at 30 degrees C.
authors.affiliation: Université de Toulouse, INSA, UPS, INP, LISBP, F-31077 Toulouse, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Emond
authors.forename: Isabelle
authors.initials: I
authors.lastname: André
authors.forename: Kais
authors.initials: K
authors.lastname: Jaziri
authors.forename: Gabrielle
authors.initials: G
authors.lastname: Potocki-Véronèse
authors.forename: Philippe
authors.initials: P
authors.lastname: Mondon
authors.forename: Khalil
authors.initials: K
authors.lastname: Bouayadi
authors.forename: Hakim
authors.initials: H
authors.lastname: Kharrat
authors.forename: Pierre
authors.initials: P
authors.lastname: Monsan
authors.forename: Magali
authors.initials: M
authors.lastname: Remaud-Simeon
mesh_terms: D001483:Base Sequence; D020650:Combinatorial Chemistry Techniques; D017931:DNA Primers; D004795:Enzyme Stability; D005964:Glucosyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006358:Hot Temperature; D008958:Models, Molecular; D016296:Mutagenesis; D011487:Protein Conformation; D015202:Protein Engineering
chemical_list: D017931:DNA Primers; D005964:Glucosyltransferases; C019700:amylosucrase