Structural insights into type III polyketide synthase CylI from cylindrocyclophane biosynthesis

Area of Science:

• Biochemistry
• Structural Biology
• Natural Product Biosynthesis

Background:

• Type III polyketide synthases (PKSs) are vital enzymes in producing diverse natural products.
• Research on type III PKSs in cyanobacteria remains limited.
• CylI is a type III PKS involved in cylindrocyclophane biosynthesis.

Purpose of the Study:

• To elucidate the structural and mechanistic properties of CylI, a cyanobacterial type III PKS.
• To understand the substrate specificity and cyclization mechanisms of CylI.
• To explore the potential for engineering CylI for novel product generation.

Main Methods:

• X-ray crystallography was used to determine the structures of apo-CylI and its complexes with substrate analogues and product.
• Site-directed mutagenesis was employed to identify key residues.
• Enzyme engineering was performed to alter cyclization specificity.

Main Results:

• The crystal structure of apo-CylI revealed unique active site-proximal elements.
• Residue N259 was identified as critical for substrate preference.
• Residue S170 was found to determine cyclization specificity, enabling a switch from aldol condensation to lactonization via mutagenesis.

Conclusions:

• This study provides molecular insights into cyanobacterial type III PKS function.
• The findings lay the groundwork for engineering CylI-like enzymes for novel natural product synthesis.
• Understanding CylI's mechanism opens possibilities for synthetic biology applications.