Brachner Andreas, Reipert Siegfried, Foisner Roland, Gotzmann Josef
Department of Medical Biochemistry, Max F. Perutz Laboratories, Vienna Biocenter, Medical University of Vienna, Dr Bohrgasse 9/3, A-1030 Vienna, Austria.
J Cell Sci. 2005 Dec 15;118(Pt 24):5797-810. doi: 10.1242/jcs.02701.
The LEM (lamina-associated polypeptide-emerin-MAN1) domain is a motif shared by a group of lamin-interacting proteins in the inner nuclear membrane (INM) and in the nucleoplasm. The LEM domain mediates binding to a DNA-crosslinking protein, barrier-to-autointegration factor (BAF). We describe a novel, ubiquitously expressed LEM domain protein, LEM2, which is structurally related to MAN1. LEM2 contains an N-terminal LEM motif, two predicted transmembrane domains and a MAN1-Src1p C-terminal (MSC) domain highly homologous to MAN1, but lacks the MAN1-specific C-terminal RNA-recognition motif. Immunofluorescence microscopy of digitonin-treated cells and subcellular fractionation identified LEM2 as a lamina-associated protein residing in the INM. LEM2 binds to the lamin C tail in vitro. Targeting of LEM2 to the nuclear envelope requires A-type lamins and is mediated by the N-terminal and transmembrane domains. Highly overexpressed LEM2 accumulates in patches at the nuclear envelope and forms membrane bridges between nuclei of adjacent cells. LEM2 structures recruit A-type lamins, emerin, MAN1 and BAF, whereas lamin B and lamin B receptor are excluded. Our data identify LEM2 as a novel A-type-lamin-associated INM protein involved in nuclear structure organization.
LEM（核纤层相关多肽-emerin-MAN1）结构域是内核膜（INM）和核质中一组与核纤层相互作用的蛋白质共有的基序。LEM结构域介导与一种DNA交联蛋白——屏障自整合因子（BAF）的结合。我们描述了一种新的、广泛表达的LEM结构域蛋白LEM2，它在结构上与MAN1相关。LEM2包含一个N端LEM基序、两个预测的跨膜结构域和一个与MAN1高度同源的MAN1-Src1p C端（MSC）结构域，但缺乏MAN1特异性的C端RNA识别基序。对洋地黄皂苷处理的细胞进行免疫荧光显微镜检查和亚细胞分级分离，确定LEM2是一种位于INM的核纤层相关蛋白。LEM2在体外与核纤层蛋白C尾部结合。将LEM2靶向核膜需要A型核纤层蛋白，并且由N端和跨膜结构域介导。高度过表达的LEM2在核膜处聚集成斑块，并在相邻细胞的细胞核之间形成膜桥。LEM2结构募集A型核纤层蛋白、emerin、MAN1和BAF，而核纤层蛋白B和核纤层蛋白B受体则被排除在外。我们的数据确定LEM2是一种参与核结构组织的新型A型核纤层蛋白相关的INM蛋白。
