ATP-binding cassette domain of eukaryotic SMC1 proteins
The structural maintenance of chromosomes (SMC) proteins are large (approximately 110 to 170 kDa), and each is arranged into five recognizable domains. Amino-acid sequence homology of SMC proteins between species is largely confined to the amino- and carboxy-terminal globular domains. The amino-terminal domain contains a 'Walker A' nucleotide-binding domain (GxxGxGKS/T, in the single-letter amino-acid code), which by mutational studies has been shown to be essential in several proteins. The carboxy-terminal domain contains a sequence (the DA-box) that resembles a 'Walker B' motif, and a motif with homology to the signature sequence of the ATP-binding cassette (ABC) family of ATPases. The sequence homology within the carboxy-terminal domain is relatively high within the SMC1-SMC4 group, whereas SMC5 and SMC6 show some divergence in both of these sequences. In eukaryotic cells, the proteins are found as heterodimers of SMC1 paired with SMC3, SMC2 with SMC4, and SMC5 with SMC6 (formerly known as Rad18).
Jiyao W et al.(2023). "The conserved domain database in 2023.",