Efficient matrix-assisted refolding of the recombinant anti-staphylococcal truncated endolysin LysKCA and its structural and enzymatic description.

The recombinant truncated endolysin LysK consisting of two catalytic domains, N-terminal CHAP and amidase-2 (LysK) was overexpressed in E. coli in the form of inclusion bodies (IBs). These IBs were dissolved in 6 M solution of urea followed by the refolding process. The refolding efficacy of the dilution and matrix-assisted renaturation method on SP Sepharose was compared at different purification stages of LysK. Solubilizate of IBs, DEAE Sepharose flowthrough, and SP Sepharose elution fractions were examined. The presence of negatively charged nucleic acids (NA) in the solution has shown a decrease in the recombinant LysK refolding yield (less than 11.5 ± 1.3% for both renaturation methods) due to their non-specific interaction with the positively charged endolysin. The renaturation efficiency of the enzyme purified from NA (SP elution fraction) was about 29.5 ± 6.7% and 28.2 ± 3.75% for dilution and matrix-assisted methods respectively. The later approach allows conducting one-step LysK refolding, purification and collection, and also noticeably cuts time and material expenses. The analysis of CD spectroscopy data of LysK, renatured on the resin matrix, revealed alpha helices and beta strands content similar to that of the modeled 3D structure. The theoretical 3D model with two predicted domains (CHAP and amidase-2) agrees well with the differential scanning calorimetry (DSC) results of the renatured LysK showing two well-resolved peaks corresponding to the two calorimetrically-revealed domains with the midpoint transition temperature (T) of 40.1 and 65.3°С. The enzyme so obtained exhibited in vitro anti-staphylococcal activity with 2.3 ± 0.45 × 10 U/mg and retained it for at least one year.