Agmatine is a neurotransmitter with anticonvulsant, anti-neurotoxic and antidepressant-like effects, in addition it has hypoglycemic actions. Agmatine is converted to putrescine and urea by agmatinase (AGM) and by an agmatinase-like protein (ALP), a new type of enzyme which is present in human and rodent brain tissues. Recombinant rat brain ALP is the only mammalian protein that exhibits significant agmatinase activity in vitro and generates putrescine under in vivo conditions. ALP, despite differing in amino acid sequence from all members of the ureohydrolase family, is strictly dependent on Mn²⁺ for catalytic activity. However, the Mn²⁺ ligands have not yet been identified due to the lack of structural information coupled with the low sequence identity that ALPs display with known ureohydrolases. In this work, we generated a structural model of the Mn²⁺ binding site of the ALP and we propose new putative Mn²⁺ ligands. Then, we cloned and expressed a sequence of 210 amino acids, here called the “central-ALP”, which include the putative ligands of Mn²⁺. The results suggest that the central-ALP is catalytically active, as agmatinase, with an unaltered K_m for agmatine and a decreased k_cat. Similar to wild-type ALP, central-ALP is activated by Mn²⁺ with a similar affinity. Besides, a simple mutant D217A, a double mutant E288A/K290A, and a triple mutant N213A/Q215A/D217A of these putative Mn²⁺ ligands result on the loss of ALP agmatinase activity. Our results indicate that the central-ALP contains the active site for agmatine hydrolysis, as well as that the residues identified are relevant for the ALP catalysis.

The thermophilic bacterium Thermus thermophilus represents a crucial genetic reservoir for exploring thermostable enzymes as valuable biocatalysts for industrial and biotechnology applications. Here, we identify, clone, and characterize Ces1-ET, Est1-ET, and Plp1-ET, three lipolytic enzymes obtained from T. thermophilus strain ET-1 isolated from El Tatio Geothermal Field in Northern Chile. To enable recombinant expression, we constructed the pTGT-1 expression system, a versatile bifunctional shuttle vector compatible with both Escherichia coli and T. thermophilus. The three thermoenzymes Ces1-ET, Est1-ET, and Plp1-ET, were successfully cloned, expressed, and purified using the pTGT-1 system, with a molecular mass of 25 kDa, 36 kDa, and 28 kDa, respectively. The recombinant purified enzymes displayed optimal temperatures at 60 °C, 80 °C, and 70 °C and optimal pH of 7.5, 9.0, and 8.0 for Ces1-ET, Est1-ET, and Plp1-ET, respectively. Functional biochemical assays revealed a broad tolerance to surfactants, detergents, divalent cations, and high salinity, relevant properties for their application in an industrial setting. These thermostable esterases expand the repertoire of thermozymes from Thermus spp., introducing pTGT-1 as an innovative tool for thermophilic protein expression and highlighting T. thermophilus strain ET-1 from El Tatio Geothermal Field as a valuable source of thermostable enzymes for industrial and biotechnology applications.

Agmatine is a biogenic amine that functions as a neurotransmitter and exhibits anticonvulsant, antineurotoxic, and antidepressant properties. It can be metabolized into putrescine and urea by canonical agmatinases or by the agmatinase-like protein (ALP), which corresponds to the C-terminal region of the LIMCH1 protein. The amino acid sequence of ALP/LIMCH1 diverges significantly from that of canonical agmatinases and lacks the conserved residues typically required for coordination with Mn²⁺, an essential cofactor for ureohydrolase activity. The three-dimensional structure of ALP/LIMCH1 remains unresolved, and predictive artificial intelligence algorithms such as AlphaFold have failed to model it reliably. As a result, the configuration of its active site and the identity of potential metal-coordinating ligands remain elusive. In this study, we purified recombinant full-length rat LIMCH1 (119.5 kDa) and a truncated ALP variant, ΔLIM-ALP (51 kDa), and analyzed their secondary structures using circular dichroism spectroscopy. Our results indicate that both proteins differ markedly from known ureohydrolases, exhibiting a high proportion of disordered regions (~60%) and β-structures (~30%). In contrast, Escherichia coli agmatinase displays a well-defined α/β/α sandwich fold. Despite these structural differences, ALP/LIMCH1 remain the only known mammalian proteins exhibiting agmatinase activity. To gain insight into the putative active site of ALP, we proposed candidate Mn²⁺-binding residues and generated single-point mutants (N213A, Q215A, D217A, E288A, K290A). Although these mutations did not significantly alter Mn²⁺ binding or its overall content in the protein samples, four mutants exhibited a decreased K_m for agmatine and a reduced V_max when normalized to protein concentration.