# Structure-Functional Examination of Cysteine Synthase A (CysK) from Limosilactobacillus reuteri LR1

## TL;DR

This study explores the structure and function of CysK from Limosilactobacillus reuteri, revealing its biochemical properties and potential for biotechnology.

## Contribution

The study provides new insights into the thermal stability and structural features of LreCysK, highlighting its biotechnological potential.

## Key findings

- LreCysK exhibits similar kinetic parameters to CysKs from E. coli and Arabidopsis thaliana.
- The enzyme's melting point increases to nearly 90°C with PLP, showing high stability.
- LreCysK is a dimer with a unique active site featuring residues like Ile50.

## Abstract

This study presents a comprehensive analysis of cysteine synthase A (CysK) from Limosilactobacillus reuteri LR1 (LreCysK), an enzyme involved in the biosynthesis of L-cysteine. This protein supports crucial cellular functions such as sulfur metabolism, antioxidant defense, detoxification, and protein synthesis. Previously, the gene encoding LreCysK was cloned, and the enzyme with His-tag on the N-terminus was obtained in active and soluble form. Here, kinetic parameters of the enzyme were determined by the previously developed high-pressure liquid chromatography (HPLC) and ninhydrin methods. It was found that LreCysK has similar KMOAS and kcat as CysKs from Escherichia coli and from the model plant Arabidopsis thaliana. The thermal stability of LreCysK was studied using differential scanning calorimetry. It was revealed that the melting point of the enzyme increases to almost 90°C when Pyridoxal-5 phosphate (PLP) is added, indicating that the stability of the enzyme complex with PLP is relatively high. Structural studies revealed that LreCysK is a dimer, and its active site is similar to those of other enzymes, but exhibits some features characteristic of lactobacilli CysKs (GISA), as well as unique residues, such as Ile50. Also, the potential biotechnological applications of LreCysK are discussed. These findings enhance our understanding of LreCysK’s biochemical versatility and its potential applications in biotechnology and medicine.