Mao Tonglin, Jin Lifeng, Li Hua, Liu Bo, Yuan Ming
State Key Laboratory of Plant Physiology and Biochemistry, Department of Plant Sciences, College of Biological Sciences, China Agricultural University, Beijing 100094, China.
Plant Physiol. 2005 Jun;138(2):654-62. doi: 10.1104/pp.104.052456. Epub 2005 May 20.
The organization and dynamics of microtubules are regulated by microtubule-associated proteins, or MAPs. In Arabidopsis (Arabidopsis thaliana), nine genes encode proteins of the evolutionarily conserved MAP65 family. We proposed that different MAP65s might have distinct roles in the interaction with microtubules. In this study, two AtMAP65 proteins, AtMAP65-1 and AtMAP65-6, were chosen to test this hypothesis in vitro. Although both fusion proteins were able to cosediment with microtubules in vitro, different properties on tubulin polymerization and microtubule bundling were observed. AtMAP65-1 was able to promote tubulin polymerization, enhance microtubule nucleation, and decrease the critical concentration for tubulin polymerization. It also induced the formation of large microtubule bundles by forming cross-bridges between microtubules evenly along the whole length of microtubules. In the presence of AtMAP65-1, microtubule bundles were more resistant to cold and dilution treatments. AtMAP65-6, however, demonstrated no activity in promoting tubulin polymerization and stabilizing preformed microtubules. AtMAP65-6 induced microtubules to form a mesh-like network with individual microtubules. Cross-bridge-like interactions were only found at regional sites between microtubules. The microtubule network induced by AtMAP65-6 was more resistant to high concentration of NaCl than the bundles induced by AtMAP65-1. Purified monospecific anti-AtMAP65-6 antibodies revealed that AtMAP65-6 was associated with mitochondria in Arabidopsis cells. It was concluded that these two MAP65 proteins were targeted to distinct sites, thus performing distinct functions in Arabidopsis cells.
微管的组织和动力学受微管相关蛋白（MAPs）调控。在拟南芥中，有九个基因编码进化上保守的MAP65家族蛋白。我们推测不同的MAP65在与微管的相互作用中可能具有不同的作用。在本研究中，选择了两种拟南芥MAP65蛋白AtMAP65-1和AtMAP65-6在体外验证这一假设。尽管两种融合蛋白在体外均能与微管共沉降，但在微管蛋白聚合和微管束集方面观察到了不同特性。AtMAP65-1能够促进微管蛋白聚合、增强微管成核，并降低微管蛋白聚合的临界浓度。它还通过在微管全长均匀地形成微管间的交叉桥来诱导大型微管束的形成。在AtMAP65-1存在的情况下，微管束对冷处理和稀释处理更具抗性。然而，AtMAP65-6在促进微管蛋白聚合和稳定已形成的微管方面没有活性。AtMAP65-6诱导微管形成由单个微管组成的网状网络。仅在微管间的局部位点发现类似交叉桥的相互作用。AtMAP65-6诱导的微管网络比AtMAP65-1诱导的微管束对高浓度NaCl更具抗性。纯化的单特异性抗AtMAP65-6抗体显示，AtMAP65-6与拟南芥细胞中的线粒体相关。得出的结论是，这两种MAP65蛋白定位于不同位点，因此在拟南芥细胞中发挥不同功能。
