Fischer I, Romano-Clarke G, Grynspan F
Department of Biochemistry, E. K. Shriver Center, Waltham, MA 02254.
Neurochem Res. 1991 Aug;16(8):891-8. doi: 10.1007/BF00965538.
Microtubule associated proteins MAP1B and MAP2 are important components of the neuronal cytoskeleton. During early development of the brain, MAP1B (340 kDa) is present as two isoforms that differ in their level of phosphorylation, while MAP2 is expressed as a single high molecular weight isoform (MAP2B, 280 kDa) and a low molecular weight form (MAP2C, 70 kDa). In this study we examined and compared the sensitivities of MAP1B and MAP2, obtained from MT preparations and brain homogenates of young rats, to degradation by calcium-activated neutral protease, calpain II. We found that in MAPs prepared from microtubules the two isoforms of MAP1B had comparable sensitivity to calpain-mediated proteolysis. Similarly, the high and low molecular weight forms of MAP2 were equally sensitive to digestion by calpain. However, although both MAPs were very susceptible to calpain-mediated proteolysis, MAP1B was more resistant to degradation by calpain than MAP2. Furthermore, the endogenous degradation of MAPs in neonate brain homogenates was calcium-dependent and inhibited by leupeptin, and the pattern of degradation products for MAP1B and MAP2 was similar to that of calpain-mediated proteolysis. These data suggest that calpain can play a role in the regulation of MAPs levels during brain development, in relation to normal neuronal differentiation and disorders associated with neurodegeneration.
微管相关蛋白MAP1B和MAP2是神经元细胞骨架的重要组成部分。在大脑早期发育过程中，MAP1B（340 kDa）以两种磷酸化水平不同的异构体形式存在，而MAP2则以单一的高分子量异构体（MAP2B，280 kDa）和低分子量形式（MAP2C，70 kDa）表达。在本研究中，我们检测并比较了从幼鼠的微管制剂和脑匀浆中获得的MAP1B和MAP2对钙激活中性蛋白酶钙蛋白酶II降解的敏感性。我们发现，在从微管制备的微管相关蛋白中，MAP1B的两种异构体对钙蛋白酶介导的蛋白水解具有相当的敏感性。同样，MAP2的高分子量和低分子量形式对钙蛋白酶的消化同样敏感。然而，尽管两种微管相关蛋白都极易受到钙蛋白酶介导的蛋白水解作用，但MAP1B比MAP2对钙蛋白酶的降解更具抗性。此外，新生脑匀浆中微管相关蛋白的内源性降解是钙依赖性的，并受到亮抑酶肽的抑制，MAP1B和MAP2的降解产物模式与钙蛋白酶介导的蛋白水解相似。这些数据表明，钙蛋白酶在大脑发育过程中MAPs水平的调节中可能发挥作用，这与正常的神经元分化以及与神经退行性变相关的疾病有关。
