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Toward the smallest active subdomain of a TIM-barrel fold: insights from a truncated α-amylase
Mamdouh Ben Ali1, Mehdi Ghram, Houda Hmani
1Laboratoire de Métabolites et de Biomolécules, Centre de Biotechnologie de Sfax, Université de Sfax, B.P. 1177, 3018 Sfax, Tunisia. mamdouh.benali@cbs.rnrt.tn
Abstract:
AmyTM is a truncated mutant of the α-amylase of Bacillus stearothermophilus US100. It has been derived from the wild type amylase gene via a reading frame shift, following a tandem duplication of the mutant primer, associated to an Adenine base deletion. AmyTM was composed of 720 nucleotides encoding 240 amino acid residues out of 549 of the wild type. The AmyTM protein was devoided of the three catalytic residues but still retains catalytic activity. It is Ca-independent maltotetraose producing amylase, optimally active at pH 6 and 60°C, under monomeric or multimeric forms. AmyTM is the smallest functional truncated TIM barrel. It contains the βαβα unit as the minimal subdomain associated to an enzymatic function. The enzymatic activity can, until now, be attributed to the presence of the whole domain B, in the structure of AmyTM. This mutant revealed, for the first time, the regeneration of a catalytic site after its abolition. This fact may be considered as the restoration of a primitive active site, which was lost in the course of evolution toward more stable domains.
Insights
Researchers engineered AmyTM, a functional truncated α-amylase, which unexpectedly regenerated its catalytic site. This smallest functional TIM barrel offers insights into primitive enzyme active site restoration.
Area of Science:
- Biochemistry
- Enzymology
- Protein Engineering
Background:
- The α-amylase from Bacillus stearothermophilus US100 is a well-studied enzyme.
- Truncated enzyme variants can provide insights into protein structure-function relationships.
- Understanding enzyme evolution and active site regeneration is crucial for protein engineering.
Purpose of the Study:
- To characterize AmyTM, a novel truncated α-amylase mutant.
- To investigate the structural and functional properties of the smallest functional TIM barrel.
- To explore the mechanism of catalytic site regeneration in a modified enzyme.
Main Methods:
- Genetic engineering to create the AmyTM mutant via reading frame shift and adenine base deletion.
- Biochemical assays to determine enzymatic activity, optimal pH, temperature, and Ca-dependency.
- Structural analysis to identify the minimal functional subdomain and active site components.
Main Results:
- AmyTM, a 240-amino acid truncated α-amylase, retains catalytic activity despite lacking key catalytic residues.
- It functions as a Ca-independent maltotetraose-producing amylase, optimal at pH 6 and 60°C.
- AmyTM represents the smallest functional truncated TIM barrel, with domain B implicated in its residual activity and catalytic site regeneration.
Conclusions:
- The AmyTM mutant demonstrates the regeneration of a catalytic site after its apparent abolition.
- This finding suggests the potential restoration of a primitive active site.
- AmyTM provides a unique model for studying enzyme evolution and the minimal requirements for enzymatic function.
