Sun2
Domain
The proximal coiled coil domain mediates trimerization required for binding to nesprins. The distal coiled coil domain is proposed to dynamically regulate the oligomeric state by locking the SUN domain in an inactive confirmation (PubMed:26688217). The coiled coil domains are proposed to be involved in load-bearing and force transmission from the cytoskeleton (By similarity).
The SUN domain may play a role in nuclear anchoring and/or migration.
Function
As a component of the LINC (LInker of Nucleoskeleton and Cytoskeleton) complex, involved in the connection between the nuclear lamina and the cytoskeleton. The nucleocytoplasmic interactions established by the LINC complex play an important role in the transmission of mechanical forces across the nuclear envelope and in nuclear movement and positioning. Specifically, SYNE2 and SUN2 assemble in arrays of transmembrane actin-associated nuclear (TAN) lines which are bound to F-actin cables and couple the nucleus to retrograde actin flow during actin-dependent nuclear movement. Required for interkinetic nuclear migration (INM) and essential for nucleokinesis and centrosome-nucleus coupling during radial neuronal migration in the cerebral cortex and during glial migration. Required for nuclear migration in retinal photoreceptor progenitors implicating association with cytoplasmic dynein-dynactin and kinesin motor complexes, and probably B-type lamins; SUN1 and SUN2 seem to act redundantly. The SUN1/2:KASH5 LINC complex couples telomeres to microtubules during meiosis; SUN1 and SUN2 seem to act at least partial redundantly. Anchors chromosome movement in the prophase of meiosis and is involved in selective gene expression of coding and non-coding RNAs needed for gametogenesis. Required for telomere attachment to nuclear envelope and gametogenesis. May also function on endocytic vesicles as a receptor for Rab5-GDP and participate in the activation of Rab5.
Post-translational modifications
The disulfide bond with SYNE2 is required for stability of the SUN2:SYNE2/KASH2 LINC complex under tensile forces though not required for the interaction. The disulfide bond is proposed to be conserved in LINC complexes involved in force transmission.
Tissue Specificity
Highly expressed in heart, placenta and muscle.
Cellular localization
- Nucleus inner membrane
- Single-pass type II membrane protein
- Nucleus envelope
- Endosome membrane
- Single-pass type II membrane protein
- Colocalizes with KASH5 at sites of telomere attachment in meiocytes.
Alternative names
Unc84b, Sun2, SUN domain-containing protein 2, Protein unc-84 homolog B, Sad1/unc-84 protein-like 2