Type II thioesterase from Streptomyces coelicolor A3(2)

Area of Science:

• Biochemistry
• Molecular Biology
• Microbiology

Background:

• Type I polyketide synthases (PKSs) are multimodular enzymes crucial for synthesizing polyketide compounds.
• Thioesterase II (TE II) genes are often found adjacent to PKS gene clusters and encode discrete proteins involved in polyketide biosynthesis.
• Distinguishing TE IIs from the fused TE I domains is important for understanding PKS pathways.

Purpose of the Study:

• To identify and characterize a novel type II thioesterase (TE II) gene, designated scoT, from Streptomyces coelicolor A3(2).
• To determine the catalytic function and functional equivalence of the ScoT protein.
• To investigate the transcriptional regulation of the scoT gene.

Main Methods:

• Gene identification and sequence analysis of scoT.
• Heterologous expression of scoT in Streptomyces fradiae to complement the tylO gene.
• Assessment of macrolide production in complemented strains.
• S1 nuclease mapping to identify the transcription start point of scoT.

Main Results:

• The scoT gene was identified and its deduced amino acid sequence showed similarity to known thioesterases, including conserved catalytic residues.
• Heterologous expression of scoT restored macrolide production in a tylO mutant, demonstrating catalytic activity.
• scoT was found to be catalytically equivalent to the TylO protein.
• S1 nuclease mapping indicated a single transcription start point for scoT, with expression limited to the transition phase of growth.

Conclusions:

• The newly identified scoT gene encodes a functional type II thioesterase (TE II) in Streptomyces coelicolor.
• The ScoT protein is catalytically equivalent to the TylO TE II, playing a role in macrolide biosynthesis.
• The expression of scoT is tightly regulated, occurring transiently during a specific growth phase.