SUNdomain

The SUN domain refers to a conserved protein domain found in the SUN family of inner nuclear membrane proteins. The name derives from the first proteins in which it was identified, Sad1 and UNC-84, and the domain is typically located toward the C-terminus of SUN proteins. The SUN domain is involved in interaction with KASH family proteins in the perinuclear space, forming a bridge across the nuclear envelope.

In cells, SUN-domain proteins are components of the linker of nucleoskeleton and cytoskeleton (LINC) complex, which connects the nucleoskeleton to the cytoskeleton. This connection enables the transfer of mechanical forces, supports nuclear positioning, and contributes to processes such as nuclear migration, centrosome positioning, and cell polarization. The SUN–KASH interaction across the perinuclear space helps coordinate nuclear shape and movement during development, division, and differentiation.

The SUN domain is widely conserved across eukaryotes and is found in diverse organisms, including fungi, plants, and animals. Many lineages possess multiple SUN proteins, often with distinct tissue or developmental expression patterns, reflecting specialization of their roles in nuclear mechanics and signaling. The domain’s conservation underlines its fundamental function in organizing the nuclear envelope and maintaining cellular architecture.

Research on SUN-domain proteins encompasses structural biology, cell biology, and developmental biology. Studies typically focus on how SUN proteins recruit and interact with KASH partners, regulate LINC complex assembly, and respond to mechanical cues. Abnormal SUN–KASH signaling can disrupt nuclear positioning and mechanotransduction, highlighting the domain’s importance for proper cell function and organismal development.