La Bella Vincenzo, Kallenbach Sacha, Pettmann Brigitte
Inserm U 382-IBDM, Campus de Luminy, Marseille 13288, France.
Biochem Biophys Res Commun. 2004 Nov 5;324(1):288-93. doi: 10.1016/j.bbrc.2004.09.057.
Spinal muscular atrophy (SMA) is an autosomal recessive disease characterized by a progressive loss of the spinal motoneurons. The SMA-determining gene has been termed survival motor neuron (SMN) and is deleted or mutated in over 98% of patients. The encoded gene product is a protein expressed as different isoforms. In particular, we showed that the rat SMN cDNA produces two isoforms with M(r) of 32 and 35kDa, both localized in nuclear coiled bodies, but the 32kDa form is also cytoplasmic, whereas the 35kDa form is also microsomal. To determine the molecular relationship between these two isoforms and potential post-translational modifications, we performed transfection experiments with a double-tagged rat SMN. Immunoblot and immunostaining studies demonstrated that the 32kDa SMN isoform derives from the full length 35kDa, through a proteolytic cleavage at the C-terminal. Furthermore, the 35kDa SMN isoform is physiologically phosphorylated in vivo. This may modulate its interaction with molecular partners, either proteins or nucleic acids.
脊髓性肌萎缩症（SMA）是一种常染色体隐性疾病，其特征为脊髓运动神经元进行性丧失。决定SMA的基因被称为生存运动神经元（SMN），超过98%的患者该基因存在缺失或突变。编码的基因产物是一种以不同异构体形式表达的蛋白质。特别是，我们发现大鼠SMN cDNA产生两种分子量分别为32kDa和35kDa的异构体，二者均定位于核卷曲体，但32kDa的形式也存在于细胞质中，而35kDa的形式也存在于微粒体中。为了确定这两种异构体之间的分子关系以及潜在的翻译后修饰，我们用双标签大鼠SMN进行了转染实验。免疫印迹和免疫染色研究表明，32kDa的SMN异构体是通过35kDa全长异构体在C末端的蛋白水解切割产生的。此外，35kDa的SMN异构体在体内发生生理性磷酸化。这可能会调节其与分子伴侣（蛋白质或核酸）的相互作用。
