Efficient spermidine production using a multi-enzyme cascade system utilizing methionine adenosyltransferase from Lactobacillus fermentum with Reduced Product Inhibition and Acidic pH Preference

Methionine adenosyltransferases (MATs; EC 2.5.1.6) are key enzymes that catalyze a crucial step in the spermidine biosynthesis pathway. Due to MAT's significant product inhibition, S-adenosylmethionine (SAM) and spermidine production faces challenges. We evaluated MATs from 20 lactic acid bacteria (LAB) to identify enzymes with acidic preference and lower susceptibility to product inhibition. Lactobacillus fermentum's MAT (LfMAT) emerged as a candidate with desirable characteristics. LfMAT exhibited strong activity in acidic environments, maintaining over 85 % activity between pH 6.0–8.5 for 60 min, with peak efficacy at pH 7.0. LfMAT produced 4.2 mM SAM from 5 mM substrate, indicating reduced product inhibition. Ultimately, using an in vitro multi-enzyme cascade system containing LfMAT, S-adenosylmethionine decarboxylase, and spermidine synthase, we successfully produced 12.9 g·L⁻¹ of spermidine. This study establishes a cascade reaction platform, offering a novel approach for the efficient synthesis of spermidine and other polyamines.