Stankewich M C, Tse W T, Peters L L, Ch'ng Y, John K M, Stabach P R, Devarajan P, Morrow J S, Lux S E
Department of Pathology, Yale University, New Haven, CT 06520, USA.
Proc Natl Acad Sci U S A. 1998 Nov 24;95(24):14158-63. doi: 10.1073/pnas.95.24.14158.
Spectrin is an important structural component of the plasma membrane skeleton. Heretofore-unidentified isoforms of spectrin also associate with Golgi and other organelles. We have discovered another member of the beta-spectrin gene family by homology searches of the GenBank databases and by 5' rapid amplification of cDNA ends of human brain cDNAs. Collectively, 7,938 nucleotides of contiguous clones are predicted to encode a 271,294-Da protein, called betaIII spectrin, with conserved actin-, protein 4.1-, and ankyrin-binding domains, membrane association domains 1 and 2, a spectrin dimer self-association site, and a pleckstrin-homology domain. betaIII spectrin transcripts are concentrated in the brain and present in the kidneys, liver, and testes and the prostate, pituitary, adrenal, and salivary glands. All of the tested tissues contain major 9.0-kb and minor 11.3-kb transcripts. The human betaIII spectrin gene (SPTBN2) maps to chromosome 11q13 and the mouse gene (Spnb3) maps to a syntenic region close to the centromere on chromosome 19. Indirect immunofluorescence studies of cultured cells using antisera specific to human betaIII spectrin reveal a Golgi-associated and punctate cytoplasmic vesicle-like distribution, suggesting that betaIII spectrin associates with intracellular organelles. This distribution overlaps that of several Golgi and vesicle markers, including mannosidase II, p58, trans-Golgi network (TGN)38, and beta-COP and is distinct from the endoplasmic reticulum markers calnexin and Bip. Liver Golgi membranes and other vesicular compartment markers cosediment in vitro with betaIII spectrin. betaIII spectrin thus constitutes a major component of the Golgi and vesicular membrane skeletons.
血影蛋白是质膜骨架的重要结构成分。此前未被鉴定的血影蛋白同工型也与高尔基体及其他细胞器相关联。我们通过对GenBank数据库进行同源性搜索以及对人脑cDNA进行5' cDNA末端快速扩增，发现了β-血影蛋白基因家族的另一个成员。连续克隆的7938个核苷酸共同预测编码一种271294道尔顿的蛋白质，称为βIII血影蛋白，它具有保守的肌动蛋白结合域、蛋白4.1结合域、锚蛋白结合域、膜结合域1和2、血影蛋白二聚体自缔合位点以及一个普列克底物蛋白同源结构域。βIII血影蛋白转录本在脑中富集，在肾脏、肝脏、睾丸以及前列腺、垂体、肾上腺和唾液腺中也有表达。所有检测的组织都含有主要的9.0 kb和次要的11.3 kb转录本。人类βIII血影蛋白基因（SPTBN2）定位于11号染色体q13区，小鼠基因（Spnb3）定位于19号染色体上靠近着丝粒的同线区域。使用针对人类βIII血影蛋白的抗血清对培养细胞进行间接免疫荧光研究，显示出与高尔基体相关的点状胞质囊泡样分布，表明βIII血影蛋白与细胞内细胞器相关联。这种分布与几种高尔基体和囊泡标记物的分布重叠，包括甘露糖苷酶II、p58、反式高尔基体网络（TGN）38和β-COP，并且与内质网标记物钙连蛋白和结合免疫球蛋白蛋白不同。肝高尔基体膜和其他囊泡区室标记物在体外与βIII血影蛋白共沉降。因此，βIII血影蛋白构成了高尔基体和囊泡膜骨架的主要成分。
