Guanidino acid hydrolysis by the human enzyme annotated as agmatinase

Abstract

Guanidino acids such as taurocyamine, guanidinobutyrate, guanidinopropionate, and guanidinoacetate have been detected in humans. However, except for guanidionacetate, which is a precursor of creatine, their metabolism and potential functions remain poorly understood. Agmatine has received considerable attention as a potential neurotransmitter and the human enzyme so far annotated as agmatinase (AGMAT) has been proposed as an important modulator of agmatine levels. However, conclusive evidence for the assigned enzymatic activity is lacking. Here we show that AGMAT hydrolyzed a range of linear guanidino acids but was virtually inactive with agmatine. Structural modelling and direct biochemical assays indicated that two naturally occurring variants differ in their substrate preferences. A negatively charged group in the substrate at the end opposing the guanidine moiety was essential for efficient catalysis, explaining why agmatine was not hydrolyzed. We suggest to rename AGMAT as guanidino acid hydrolase (GDAH). Additionally, we demonstrate that the GDAH substrates taurocyamine, guanidinobutyrate and guanidinopropionate were produced by human glycine amidinotransferase (GATM). The presented findings show for the first time an enzymatic activity for GDAH/AGMAT. Since agmatine has frequently been proposed as an endogenous neurotransmitter, the current findings clarify important aspects of the metabolism of agmatine and guanidino acid derivatives in humans.

Insights into the action of the pharmaceutical metformin: Targeted inhibition of the gut microbial enzyme agmatinase

“…There are three ureohydrolase homologs in humans which include arginases, ARG1 and ARG2 as well as the enzyme AGMAT that is active on guanidino acids like 4-guanidinobutyrate. 19 , 20 , 21 The largest cluster, cluster 2, of gut sequences in the SSN contains a separate subfamily of agmatinase enzymes which have been found to be Ni 2+ , Co 2+ , or Fe 2+ dependent and are divergent from the E. coli agmatinase which is Mn 2+ dependent ( Figure 1 C). This was determined when characterizing a sequence from this divergent cluster, from the gut microbe, Clostridium butyricum (CbAGM), with 32% sequence identity to EcAGM, which was most activated with the addition of Ni 2+ but not Mn 2+ cations ( Figure S1 ).…”

“…Truncation variants ARG2 Δ 1-24 /Δ 331-354 and AGMAT Δ 1-35 were made as done in prior studies and codon-optimized, cloned in the same procedure as above. 20 , 21 …”