C-S bond cleavage by a polyketide synthase domain

Area of Science:

• Biochemistry
• Natural Product Biosynthesis
• Molecular Biology

Background:

• Leinamycin (LNM) is a sulfur-containing antitumor antibiotic with a unique structure essential for DNA alkylation.
• The biosynthesis of LNM involves a hybrid nonribosomal peptide synthetase (NRPS)-polyketide synthase (PKS) system.
• The origin of sulfur at the C-3 position of LNM remained uncharacterized.

Purpose of the Study:

• To elucidate the mechanism of sulfur incorporation into leinamycin.
• To identify the enzyme responsible for introducing sulfur at the C-3 position.
• To characterize the novel enzymatic domain involved in this process.

Main Methods:

• Bioinformatic analysis of the LNM gene cluster, specifically identifying a pyridoxal phosphate (PLP)-dependent domain (LnmJ-SH).
• In vitro enzymatic assays using L-cysteine and its analogs as substrates for the LnmJ-SH domain.
• Characterization of the catalytic mechanism, including PLP-dependent β-elimination.

Main Results:

• A novel PLP-dependent cysteine lyase (SH) domain (LnmJ-SH) was identified within the PKS module of LnmJ.
• The LnmJ-SH domain catalyzes C-S bond cleavage, utilizing L-cysteine to establish the sulfur incorporation at C-3 of LNM.
• This domain represents a new family of PKS domains with unique C-S bond cleavage activity.

Conclusions:

• L-cysteine is the direct precursor for sulfur incorporation at the C-3 position of leinamycin.
• The LnmJ-SH domain is a novel enzyme family expanding the known chemistry and enzymology of PKSs.
• The LnmJ-SH domain offers potential for engineering PKSs to synthesize novel sulfur-containing polyketides.