Metagenomic Type IV Aminotransferases Active toward (R)-Methylbenzylamine

Abstract

Aminotransferases (ATs) are pyridoxal 5′-phosphate-dependent enzymes that catalyze the reversible transfer of an amino group from an amino donor to a keto substrate. ATs are promising biocatalysts that are replacing traditional chemical routes for the production of chiral amines. In this study, an in silico-screening of a metagenomic library isolated from the Curonian Lagoon identified 11 full-length fold type IV aminotransferases that were successfully expressed and used for substrate profiling. Three of them (AT-872, AT-1132, and AT-4421) were active toward (R)-methylbenzylamine. Purified proteins showed activity with L- and D-amino acids and various aromatic compounds such as (R)-1-aminotetraline. AT-872 and AT-1132 exhibited thermostability and retained about 55% and 80% of their activities, respectively, even after 24 h of incubation at 50 °C. Active site modeling revealed that AT-872 and AT-4421 have an unusual active site environment similar to the AT of Haliscomenobacter hydrossis, while AT-1132 appeared to be structurally related to the AT from thermophilic archaea Geoglobus acetivorans. Thus, we have identified and characterized PLP fold type IV ATs that were active toward both amino acids and a variety of (R)-amines.