Kite Proteins: a Superfamily of SMC/Kleisin Partners Conserved Across Bacteria, Archaea, and Eukaryotes

• Published in: Structure (London) 2015-12, Vol.23 (12), p.2183-2190
• Main Authors: Palecek, Jan J., Gruber, Stephan
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Archaeal Proteins - chemistry; Archaeal Proteins - genetics; Archaeal Proteins - metabolism; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Cell Cycle Proteins - chemistry; Cell Cycle Proteins - genetics; Cell Cycle Proteins - metabolism; chromosome segregation; cohesin; cohesion; condensation; condensin; Conserved Sequence; Kinesin - chemistry; Kinesin - metabolism; kite proteins; kleisin; MAGE; MksBEF; Molecular Sequence Data; MukBEF; replication; SMC; Smc/ScpAB; Smc5/6; structural maintenance of chromosomes; winged helix domains
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2015.10.004

SMC/kleisin complexes form elongated annular structures, which are critical for chromosome segregation, genome maintenance, and the regulation of gene expression. We describe marked structural similarities between bacterial and eukaryotic SMC/kleisin partner proteins (designated here as “kite” proteins for kleisin interacting tandem winged-helix (WH) elements of SMC complexes). Kite proteins are integral parts of all prokaryotic SMC complexes and Smc5/6 but not cohesin and condensin. They are made up of tandem WH domains, form homo- or heterodimers via their amino-terminal WH domain, and they associate with the central part of a kleisin subunit. In placental mammals, the kite subunit NSE3 gave rise to several (>60) kite-related proteins, named MAGE, many of which encode tumor- and testis-specific antigens. Based on architectural rather than sequence similarity, we propose an adapted model for the evolution of the SMC protein complexes and discuss potential functional similarities between bacterial Smc/ScpAB and eukaryotic Smc5/6. [Display omitted] •Smc5/6 and bacterial SMC complexes harbor structurally related kite subunits•Kite proteins comprise tandem WH domains that assemble into homo- and heterodimers•Kite dimers associate with a respective kleisin subunit•Smc5/6 and bacterial Smc/ScpAB might perform similar functions and share mechanisms Three distinct SMC complexes are needed for proper chromosome maintenance and segregation in eukaryotes. Palecek and Gruber reveal that Smc5/6 complexes, but not cohesin and condensin, share structurally conserved tandem WH domain subunits with their prokaryotic relatives. Potential functional and evolutionary implications are discussed.