Ferralli J, Doll T, Matus A
Friedrich Miescher Institute, Basel, Switzerland.
J Cell Sci. 1994 Nov;107 ( Pt 11):3115-25. doi: 10.1242/jcs.107.11.3115.
Microtubule-associated protein 2 (MAP2) is an abundant neuron-specific protein that binds to microtubules through a domain near its carboxyl terminus that contains either three or four similar repeats of a 31 amino acid motif. When expressed in non-neuronal cells by transfection MAP2 stabilises microtubules and induces their rearrangement into long bundles that are capable of supporting process outgrowth. To investigate which elements in the MAP2 sequence are involved in these functions we have constructed a series of deletion mutants of the short embryonic form of MAP2, MAP2c, and transfected them into non-neuronal cells. This showed that the strength of binding to microtubules increased with the number of repeats present in the construct. However, the repeat domain itself was insufficient for microtubule binding, which required in addition contiguous sequences either amino-terminal or carboxyl-terminal to the repeats themselves. Particularly on the amino-terminal side of the repeats, where there is a proline-rich domain, step-wise increases in the length of neighbouring sequence produced a gradual increase in microtubule binding. The apparent strength of binding to microtubules produced by mutant MAP2 forms was further correlated with the degree of bundling they induced as well as with the ability of the resulting microtubules to support process outgrowth. These results indicate that the interaction of MAP2 with microtubules is mediated by the combined action of several weak binding sites, including each of the repeat motifs and elements in the sequences on either side of them, whose additive effect produces the strong binding of the native MAP2 molecule. The results further indicate that both the bundling and stiffening of microtubules by MAP2 are correlated with the strength of its binding to them and suggest that these properties are a direct result of microtubule stabilisation.
微管相关蛋白2（MAP2）是一种丰富的神经元特异性蛋白，它通过其羧基末端附近的一个结构域与微管结合，该结构域包含31个氨基酸基序的三个或四个相似重复序列。当通过转染在非神经元细胞中表达时，MAP2可稳定微管并诱导它们重排成能够支持突起生长的长束。为了研究MAP2序列中的哪些元件参与这些功能，我们构建了一系列MAP2短胚胎形式MAP2c的缺失突变体，并将它们转染到非神经元细胞中。这表明与微管结合的强度随着构建体中重复序列的数量增加而增加。然而，重复结构域本身不足以结合微管，还需要重复序列自身氨基末端或羧基末端的相邻序列。特别是在重复序列的氨基末端一侧，那里有一个富含脯氨酸的结构域，相邻序列长度的逐步增加会导致微管结合逐渐增加。突变型MAP2形式产生的与微管结合的表观强度还与它们诱导的成束程度以及所得微管支持突起生长的能力相关。这些结果表明，MAP2与微管的相互作用是由几个弱结合位点的共同作用介导的，包括每个重复基序及其两侧序列中的元件，它们的累加效应产生了天然MAP2分子的强结合。结果还表明，MAP2对微管的成束和硬化作用均与其与微管的结合强度相关，并表明这些特性是微管稳定化的直接结果。
