7vo1

Publication Abstract from PubMed

Ornithine delta-aminotransferase (Orn-AT) activity was detected for the enzyme annotated as a gamma-aminobutyrate aminotransferase encoded by PH1423 gene from Pyrococcus horikoshii OT-3. Crystal structures of this novel archaeal omega-aminotransferase were determined for the enzyme in complex with pyridoxal 5'-phosphate (PLP), in complex with PLP and l-ornithine (l-Orn), and in complex with N-(5'-phosphopyridoxyl)-l-glutamate (PLP-l-Glu). Although the sequence identity was relatively low (28%), the main-chain coordinates of P. horikoshii Orn-AT monomer showed notable similarity to those of human Orn-AT. However, the residues recognizing the alpha-amino group of l-Orn differ between the two enzymes. In human Orn-AT, Tyr55 and Tyr85 recognize the alpha-amino group, whereas the side chains of Thr92* and Asp93*, which arise from a loop in the neighboring subunit, form hydrogen bonds with the alpha-amino group of the substrate in P. horikoshii enzyme. Site-directed mutagenesis suggested that Asp93* plays critical roles in maintaining high affinity for the substrate. This study provides new insight into the substrate binding of a novel type of Orn-AT. Moreover, the structure of the enzyme with the reaction-intermediate analogue PLP-l-Glu bound provides the first structural evidence for the "Glu switch" mechanism in the dual substrate specificity of Orn-AT.

Crystal structure of a novel type of ornithine delta-aminotransferase from the hyperthermophilic archaeon Pyrococcus horikoshii.,Kawakami R, Ohshida T, Hayashi J, Yoneda K, Furumoto T, Ohshima T, Sakuraba H Int J Biol Macromol. 2022 May 31;208:731-740. doi:, 10.1016/j.ijbiomac.2022.03.114. Epub 2022 Mar 23. PMID:35337912^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.