Comparative analysis of the active sites of orthologous endolysins of the Escherichia lytic bacteriophages T5, RB43, and RB49.

The methods of solution NMR, circular dichroism (CD), and differential scanning calorimetry (DSC) were used to study two zinc-containing L-alanyl-D-glutamate peptidases - endolysins of the pseudo T-even myoviruses RB43 and RB49 (EndoRB43 and EndoRB49, respectively), which are orthologous to the EndoT5, which is a zinc-containing L-alanyl-D-glutamate peptidase of the T5 siphovirus. The spatial conservation of the Zn2+-binding sites for the enzymes EndoT5, EndoRB43, and EndoRB49 was established, and the key role of Zn2+ ions in the stabilization of the spatial structures of these three peptidases was confirmed. We are showing here that the binding of the Zn2+ ion in the active center of EndoRB49 peptidase causes conformational rearrangements similar to those observed in the EndoT5 peptidase upon binding of Zn2+ and Ca2+ ions and lead to the formation of a catalytically active form of the enzyme. Therefore, the binding of the Zn2+ ion to the active site of EndoRB49 peptidase is a necessary and sufficient condition for functioning of this protein.

On the roles of calcium and zinc ions in the formation of a catalytically active form of the metalloenzyme, l-alanyl-d-glutamate peptidase of the bacteriophage T5 (EndoT5).

Structural consequences of the binding of metal ions (regulatory Ca2+ and catalytic Zn2+) to the metalloenzyme l-alanyl-d-glutamate peptidase of the bacteriophage T5 (Endo T5) and some of its analogues containing single amino acid substitutions in the active center were analyzed by nuclear magnetic resonance (NMR), circular dichroism (CD) and calorimetry. Analyses revealed that the native EndoT5 undergoes strong structural rearrangements as a result of Zn2+ binding. This structural rearrangement resulting in the formation of an active enzyme is completed by the Ca2+ binding. In this case, the NMR spectra uncover the tautomerism of the NH protons of histidine imidazoles responsible for the Zn2+ coordination. For the EndoT5 analogues with point substitutions in the Ca2+-binding site, similar conformational rearrangements are observed upon Zn2+ binding. However, no characteristic changes in the NMR spectra associated with the Ca2+ binding were detected. The roles of the proton exchange in the process of Ca2+-induced activation of the enzymatic activity of EndoT5 is discussed.

Effect of C-terminal His-tag and purification routine on the activity and structure of the metalloenzyme, l-alanyl-d-glutamate peptidase of the bacteriophage T5.

In this work, we studied the effect of the C-terminally attached poly-histidine tag (His-tag), as well as the peculiarities of the protein purification procedure by the immobilized metal affinity chromatography (IMAC) on the activity and structure of the metalloenzyme, l-alanyl-d-glutamate peptidase of bacteriophage T5 (EndoT5), whose zinc binding site and catalytic aspartate are located near the C-terminus. By itself, His-tag did not have a significant effect on either activity or folding of the polypeptide chain, nor on the binding of zinc and calcium ions to the protein. However, the His-tagged EndoT5 samples had low shelf-life, with storage of these samples resulting in an increased propensity for protein self-association and decreased enzymatic activity of EndoT5. Furthermore, disastrous effects on the activity of the enzyme were exerted by the presence of imidazole and nickel ions accompanying metal chelate chromatography. The activity of the protein can be restored by thorough washing off of these low molecular impurities via the prolonged dialysis of the His-tagged EndoT5 samples at the specifically elaborated conditions.