SMC2

Smc2, also called SMC2, stands for Structural Maintenance of Chromosomes protein 2. It is a core component of the condensin protein complexes that drive chromosome condensation and structural organization in eukaryotic cells, enabling proper chromosome segregation during mitosis and meiosis.

SMC2 proteins are large, modular molecules characterized by an N-terminal ATPase domain and a C-terminal ATPase domain that come together to form a functional ATPase “head.” These heads are connected by long coiled-coil regions and paired with a partner SMC protein via a hinge domain to form a V-shaped heterodimer. In condensin, SMC2 pairs with SMC4 to establish the condensin core, which then associates with non-SMC subunits to execute its functions.

In higher eukaryotes, two distinct condensin complexes exist: condensin I and condensin II. In both complexes, SMC2 pairs with SMC4. The non-SMC subunits differ between the two forms (condensin I includes CAP-D2, CAP-G, CAP-H; condensin II includes CAP-D3, CAP-G2, CAP-H2), contributing to distinct timing and localization patterns of condensation during the cell cycle.

Functionally, condensin complexes reorganize chromatin into condensed chromosomes, facilitating proper chromosome condensation during prophase and ensuring accurate segregation during mitosis and meiosis. SMC2 activity is regulated by cell-cycle kinases and other factors, and it also participates in DNA repair and replication stress responses, contributing to genome stability.

SMC2 is highly conserved across eukaryotes, underscoring its essential role in chromosome architecture. Disruption of SMC2 or condensin function leads to chromosome mis-segregation, genome instability, and developmental defects in many organisms.