| Primary Identifier | IPR024188 | Type | Family |
| Short Name | GltB |
| description | Glutamate synthase (GOGAT, GltS) is a complex iron-sulphur flavoprotein that catalyses the reductive synthesis of L-glutamate from 2-oxoglutarate (2-OG) and L-glutamine via intramolecular channeling of ammonia, a reaction in the bacterial, yeast and plant pathways for ammonia assimilation []. GOGAT is a multifunctional enzyme that functions through three distinct active centres carrying out multiple reaction steps: L-glutamine hydrolysis, conversion of 2-oxoglutarate into L-glutamate, and electron uptake from an electron donor [].There are four classes of glutamate synthase (GOGAT) [], []:1. Bacterial NADPH-dependent GOGAT (NADPH-GOGAT, ). This standard bacterial NADPH-GOGAT (GltS) is composed of a large (alpha, GltB) subunit, and a small (beta, GltD) subunit.2. Ferredoxin-dependent GOGAT in cyanobacteria and plants (Fd-GOGAT from photosynthetic cells, ) displays a single-subunit structure corresponding to the large bacterial subunit.3. Pyridine-linked GOGAT in both photosynthetic and nonphotosynthetic eukaryotes (eukaryotic GOGAT or NADH-GOGAT, ) displays a single-subunit structure corresponding to the fusion of the small and the large bacterial subunits. 4. The archaeal type with stand-alone proteins corresponding to the N-terminal, FMN-binding, and the C-terminal domains of the large subunit and to the small subunit.The large (alpha, GltB) subunit of bacterial glutamate synthase (GOGAT) consists of three domains: the N-terminal amidotransferase domain (), the central domain, and the C-terminal domain (). This entry represents a stand-alone version of the central domain. The stand-alone form occurs in the archaeal-type of GOGAT, where the large subunit is represented by three separate proteins, corresponding to the three domains of the "standard"bacterial enzyme [].The second (central) domain of the bacterial GOGAT large subunit consists of a linker domain and the FMN-binding domain (). The FMN-binding domain has a beta/alpha barrel topology. In this domain, the 2-iminoglutarate intermediate, formed upon the addition of ammonia onto 2-oxoglutarate, is reduced by the FMN cofactor producing the second molecule of L-glutamate []. This domain also contains the enzyme 3Fe-4S cluster [].All members of this entry contain the FMN-binding domain. However, they lack the linker domain, and some have 1-3 copies of (4Fe-4S binding domain) in the N-terminal region.Originally, only the ORF encoding the central domain of GOGAT was recognised and annotated as GltB in archaea, and the rest of the large subunit was thought to be missing, which may lead to some misannotations []. This led to speculations that the archaeal form of the GOGAT large subunit is the ancestral minimum form of the enzyme. Later analysis showed, however, that in all archaea where the large subunit has been found, its entire sequence is represented by three separate ORFs []. |
