title: A natural variant of Bacillus licheniformis alpha-amylase isolated from flour mill wastewaters sheds light on the origin of high thermostability.
abstract: OBJECTIVE
  Understanding the origin of high thermostability exhibited by the alpha-amylase produced by a natural strain of Bacillus licheniformis.
  
  
  RESULTS
  The MSH320 alpha-amylase gene has been cloned from a native strain of B. licheniformis isolated from flour mill wastewaters in Kashan, central Iran, and its nucleotide sequence was determined (GenBank Accession Number AF438149). Whereas previously cloned B. licheniformisalpha-amylase (BLA) genes are nearly identical, the MSH320 gene coding sequence presents only 93% identity with the reference 'wild-type' BLA gene, most of the nucleotide changes leading to silent mutations. Amino acid substitutions occurred at 19 of the 483 residues of the matured protein, distributed all along the protein sequence. Nevertheless, the natural BLA variant presents thermoinactivation kinetics similar to that of the reference BLA. Protein modelling and structural predictions at the substitution sites suggest that half of the mutations may have a significant stabilizing or destabilizing effect on the protein structure. Compensatory mutations thus occurred in the natural variant in order to maintain thermostability to the level of the reference enzyme.
  
  
  CONCLUSIONS
  The exceptional high thermostability of BLA, although produced by a nonthermophilic organism, is not fortuitous but subject to a selective pressure still at work in natural environments.
  
  
  CONCLUSIONS
  BLA thermal performances are not naturally maximized and can be substantially improved by protein engineering.
authors.affiliation: Institute of Biochemistry and Biophysics, Faculty of Sciences, University of Tehran, Tehran, I.R. Iran. hoseini@ibb.ut.ac.ir
authors.forename: M
authors.initials: M
authors.lastname: Shahhoseini
authors.forename: A-A
authors.initials: AA
authors.lastname: Ziaee
authors.forename: A-A
authors.initials: AA
authors.lastname: Pourbabai
authors.forename: N
authors.initials: N
authors.lastname: Ghaemi
authors.forename: N
authors.initials: N
authors.lastname: Declerck
mesh_terms: D001407:Bacillus / Q000201:enzymology*; D001483:Base Sequence; D005433:Flour; D006358:Hot Temperature; D007220:Industrial Waste; D007221:Industry; D008969:Molecular Sequence Data; D009154:Mutation; D016415:Sequence Alignment; D038301:Virus Inactivation; D000516:alpha-Amylases / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism
chemical_list: D007220:Industrial Waste; D000516:alpha-Amylases; C501919:alpha-amylase, Bacillus licheniformis