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Bacillus subtilis X-23 produces two alpha-amylase forms, Ba-L and Ba-S, from a single gene. Despite structural differences, both enzymes exhibit similar functionality, with Ba-S showing enhanced thermal stability.

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Area of Science:

  • Enzymology
  • Protein Biochemistry
  • Microbial Genetics

Background:

  • Bacillus subtilis X-23 secretes alpha-amylases, enzymes crucial for starch hydrolysis.
  • Two forms, complete (Ba-L) and truncated (Ba-S), were identified, suggesting post-translational modification or differential expression.

Purpose of the Study:

  • To characterize the structural and functional relationship between Ba-L and Ba-S alpha-amylases.
  • To investigate the origin and implications of Ba-S formation from Ba-L.

Main Methods:

  • Purification of Ba-L and Ba-S alpha-amylases.
  • Determination of amino- and carboxyl-terminal amino acid sequences.
  • Nucleotide sequencing of the alpha-amylase gene.
  • Genomic Southern and Western blot analyses.
  • Enzymatic activity assays, including thermal stability and raw starch binding.
  • Secondary and predicted three-dimensional structure analysis.

Main Results:

  • Ba-S is a carboxyl-terminally truncated form of Ba-L, lacking 186 amino acid residues.
  • Both enzyme forms originate from the same gene, with truncation occurring during B. subtilis X-23 cultivation.
  • Despite a 28% reduction in primary structure, Ba-S retains essential functional domains (A, B, C) and exhibits similar enzymatic characteristics to Ba-L, with higher thermal stability.

Conclusions:

  • The alpha-amylase from B. subtilis X-23 exists in two forms, Ba-L and Ba-S, derived from a single gene.
  • The truncation event does not significantly impair core enzymatic functions but enhances thermal stability.
  • Ba-S represents a functionally conserved, more thermostable variant of the alpha-amylase.