Studies on the interaction of Escherichia coli agmatinase with manganese ions: structural and kinetic studies of the H126N and H151N variants

Insight on the interaction of an agmatinase-like protein with Mn2+ activator ions

“…3). While these data alone do not identify histidine residues that may play a particular function in Mn 2+ binding they do indicate that ALP behaves with respect to thermal activation similar to other agmatinases and arginases, for which these data were interpreted in terms of binding of a second Mn 2+ ion to form an optimally active binuclear metal ion center in the active site [17,18]. Thus, despite the absence of sequence homology between those enzymes and ALP the above incubation experiments with Mn 2+ support the model where a catalytically optimal binuclear center in ALP is formed upon the thermal incubation with Mn 2+ .…”

“…Adding extra Mn 2+ leads to a further increase in activity but the metal ion stoichiometry of the more active form could not be ascertained as dialysis returned the catalytic activity and metal ion stoichiometry to their initial values. However, since bacterial agmatinases and the related arginases contain a bimetallic Mn 2+ center in their active sites [17,18,20,21] it is plausible to assume that the same may thus be the case for ALP. Due to the lack of apparent sequence homology between ALP and other agmatinases and arginases it is not possible to identify possible Mn 2+ ligands in the ALP active site by sequence alignments or homology modeling.…”

“…In order to probe the role of these histidine residues further the thermostability of the mutants was investigated, as a characteristic feature of agmatinases and arginases is their increase in activity upon incubation at high temperatures in presence of excess Mn 2+ [17,18]. Fig.…”

“…The latter prevents an identification of possible ligands based on sequence alignments. Aspartate and histidine residues are generally used as ligands for the catalytically essential Mn 2+ cofactors and substrates like agmatine and arginine [17,18]. ALP contains 23 aspartate residues but only five histidine residues in its amino acid sequence.…”

Insights into the Mn2+ Binding Site in the Agmatinase-Like Protein (ALP): A Critical Enzyme for the Regulation of Agmatine Levels in Mammals

“…These findings are in agreement with observations performed for ureohydrolases, such as the rat and human arginase, and the E. coli agmatinase. For those enzymes, the mutation of one residue coordinating Mn 2+ causes partial or total loss of the enzymatic activity [43,44]. For example, on E. coli agmatinase, the mutation of the ligand H126N reduced agmatinase activity by 50%, while the mutation H151N produced a total loss of activity [44].…”