Obg is a unique family of high-molecular mass GTPases conserved from bacteria to eukaryotes. In bacteria, Obg is essential for cellular growth, sporulation, and differentiation. These proteins comprises three domains; the N-terminal, guanine nucleotide-binding (G domain), and C-terminal domains. Structural domains comprising this superfamily share the structure of the N-terminal domain, also known as the GTP1/OBG domain as it presents the OBG fold, formed by three glycine-rich regions inserted into a small 8-stranded beta-sandwich. These regions form six left-handed collagen-like helices packed and H-bonded together.

GTP-binding proteins such as the murine DRG protein, GTP1 protein from Schizosaccharomyces pombe, OBG protein from Bacillus subtilis contain characteristic GTP-binding motifs and are similar to each other, but they do not share sequence similarity to other GTP-binding proteins, and have therefore been classed as a novel group, the GTP1/OBG family. For now, the functions of these proteins is uncertain, but they have been shown to be important in development and normal cell metabolism PMID:8462872,PMID:2537815.