SMCProteinen

SMCProteinen, or SMC proteins, are a family of highly conserved ATPases that organize and maintain chromosome structure across life forms. They are found in bacteria, archaea, and eukaryotes, where they function alone or as part of larger multisubunit complexes. Each SMC protein has a long central coiled-coil region connecting an N-terminal and a C-terminal ATPase head, forming a V-shaped molecule that can enclose DNA through a dynamic ATP-dependent cycle.

In bacteria and archaea, a single SMC protein typically forms a homodimer with partner non-SMC proteins to condense and organize the chromosome during replication and segregation. In eukaryotes, SMC proteins assemble into three major complexes with distinct roles in chromosome management: cohesin, condensin, and the SMC5/6 complex. Cohesin comprises SMC1 and SMC3 together with non-SMC subunits (kleisins and SA proteins) and mediates sister chromatid cohesion, DNA repair, and the regulation of chromatin architecture. Condensin consists of SMC2 and SMC4 with regulatory non-SMC subunits and drives chromosome condensation during mitosis, while contributing to higher-order genome organization. The SMC5/6 complex, containing SMC5 and SMC6 with additional non-SMC components, participates in DNA repair, replication fork maintenance, and genome stability.

The activity of SMC proteins depends on ATP binding and hydrolysis at the head domains, which induces conformational changes that promote DNA engagement and release. Their function is tightly regulated by loading factors and other regulatory proteins that control chromosome association, timing, and activity. SMC proteins are essential for chromosome segregation, genome integrity, and proper cell division.