Inner nuclear membrane proteins

Inner nuclear membrane (INM) proteins are proteins that are embedded in or associated with the inner membrane of the nuclear envelope (NE). There are about 60 INM proteins, most of which are poorly characterized with respect to structure and function. Among the few well-characterized INM proteins are lamin B receptor (LBR), the lamina-associated polypeptide 1 (LAP1), the lamina-associated polypeptide-2 (LAP2), emerin and MAN1.

There have been identified several integral nuclear membrane proteins of different size and structure. It is proposed that they share some structural features with respect to nucleoplasmic domain(s) and lipid-soluble domain(s). Some INM proteins contain common protein domain structures, and can thus be categorised into known protein domain families. These include the LEM-, SUN-, and KASH-domain families. Members of the LEM-domain family play a part in chromatin organisation. SUN- and KASH-domains participate in linking the cytoskeleton and nucleoskeleton through the LINC complex.

Lamins and chromatin found at the nuclear envelope are organised with the assistance of proteins embedded in the INM. INM proteins also aid in organization of nuclear pore complexes (NPCs). The protein mPom121 is targeted to the INM and is necessary for NPC formation. Proteins containing the LEM domain, such as emerin, LAP2β and MAN1, seem to have a number of roles. They interact with the barrier-to-autointegration factor (BAF). and help to repress gene expression, both by tethering specific genomic regions to the nuclear periphery, and by interaction with histone deacetylase (HDAC) 3.

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