Characteristics of two forms of alpha-amylases and structural implication

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.