X-ray diffraction studies have revealed that the structure of Halothermothrix orenii SPS belongs to the GT-B fold family. Like other GT-B proteins, SPS contains two Rossmann fold domains that are named the A domain and the B domain. Generally, the structure of these domains are somewhat similar, as both contain central beta sheets that are surrounded by alpha helices. However, the A domain consists of eight parallel beta strands and seven alpha helices while the B domain contains six parallel beta strands and nine alpha helices. These domains are joined by residue loops to form a substrate binding cleft, where the glucosyl group acceptor binds.
