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. 'Walker A' forms a loop that binds to the alpha and beta phosphates of di- and tri-nucleotides.
The carboxy-terminal domain contains a sequence (the DA-box) that resembles a ' Walker B' motif ( thought to coordinate the Mg2+ ion or polarize the attacking water molecule in ATP hydrolysis like the switch region), and a motif with homology to the signature sequence of the ATP-binding cassette (ABC) family of ATPases, also called Walker C motif or linker peptide. Thought to be involved in ATP hydrolysis as a gamma phosphate sensor and/or as a signal to the membrane spanning domains.
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).

3D STRUCTURE

To visualize the structure you need Cn3D, a web browser application that allows you to view 3-dimensional structures from NCBI's Entrez retrieval service.
To dowload the software, click here.

Smc1 structure