beta-strand (B) domain of archaeal GINS complex protein Gins23
The GINS (named from the Japanese go-ichi-ni-san, meaning 5-1-2-3 for the Sld5, Psf1, Psf2, and Psf3 subunits) complex is involved in both initiation and elongation stages of eukaryotic chromosome replication, with GINS being the component that most likely serves as the replicative helicase that unwinds duplex DNA ahead of the moving replication fork. In archaeal DNA replication initiation, homo-hexameric MCM (mini-chromosome maintenance) unwinds the template double-stranded DNA to form the replication fork. MCM is activated by two proteins GINS and GAN (GINS-associated nuclease), which constitute the 'CMG' unwindosome complex together with the MCM core. While eukaryotic GINS complex is a tetrameric arrangement of four subunits Sld5, Psf1, Psf2 and Psf3, the archaeal complex consists of two different proteins, namely Gins51 and Gins23, and forms either an alpha2beta2-type heterotetramer composed of Gins51 and Gins23, or a Gins51-only alpha4-type homotetramer. The archaeal Gins23, as well as eukaryotic Psf2 and Psf3, have the alpha-helical (A) domain at the C-terminus and the beta-strand domain (B) at the N-terminus; this arrangement is called BAtype. The locations and contributions of the archaeal Gins subunit B domain to the tetramer formation, imply the possibility that the archaeal and eukaryotic GINS complexes contribute to DNA unwinding reactions by significantly different mechanisms in terms of the atomic details. This model represents the B-domain of archaeal Gins23.
Structure:3ANW: Thermococcus kodakarensis GINS complex subunit interface between Gins51 and Gins23, contacts at 4.0A - View structure with Cn3D
Comment:The different archaeal and eukaryotic GINS subunit interfaces imply the possibility that the archaeal and eukaryotic Gins complexes contribute to DNA unwinding reactions by significantly different mechanisms in terms of the atomic details.