Penzes P, Johnson R C, Alam M R, Kambampati V, Mains R E, Eipper B A
Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
J Biol Chem. 2000 Mar 3;275(9):6395-403. doi: 10.1074/jbc.275.9.6395.
Communication between membranes and the actin cytoskeleton is an important aspect of neuronal function. Regulators of actin cytoskeletal dynamics include the Rho-like small GTP-binding proteins and their exchange factors. Kalirin is a brain-specific protein, first identified through its interaction with peptidylglycine-alpha-amidating monooxygenase. In this study, we cloned rat Kalirin-7, a 7-kilobase mRNA form of Kalirin. Kalirin-7 contains nine spectrin-like repeats, a Dbl homology domain, and a pleckstrin homology domain. We found that the majority of Kalirin-7 protein is associated with synaptosomal membranes, but a fraction is cytosolic. We also detected higher molecular weight Kalirin proteins. In rat cerebral cortex, Kalirin-7 is highly enriched in the postsynaptic density fraction. In primary cultures of neurons, Kalirin-7 is detected in spine-like structures, while other forms of Kalirin are visualized in the cell soma and throughout the neurites. Kalirin-7 and its Dbl homology-pleckstrin homology domain induce formation of lamellipodia and membrane ruffling, when transiently expressed in fibroblasts, indicative of Rac1 activation. Using Rac1, the Dbl homology-pleckstrin homology domain catalyzed the in vitro exchange of bound GDP with GTP. Kalirin-7 is the first guanine-nucleotide exchange factor identified in the postsynaptic density, where it is positioned optimally to regulate signal transduction pathways connecting membrane proteins and the actin cytoskeleton.
膜与肌动蛋白细胞骨架之间的通讯是神经元功能的一个重要方面。肌动蛋白细胞骨架动力学的调节因子包括Rho样小GTP结合蛋白及其交换因子。Kalirin是一种脑特异性蛋白，最初是通过其与肽基甘氨酸-α-酰胺化单加氧酶的相互作用而被鉴定出来的。在本研究中，我们克隆了大鼠Kalirin-7，它是Kalirin的一种7千碱基的mRNA形式。Kalirin-7包含九个血影蛋白样重复序列、一个Dbl同源结构域和一个普列克底物蛋白同源结构域。我们发现，大多数Kalirin-7蛋白与突触体膜相关，但有一部分是胞质的。我们还检测到了分子量更高的Kalirin蛋白。在大鼠大脑皮层中，Kalirin-7在突触后致密部分高度富集。在神经元的原代培养物中，在棘状结构中检测到Kalirin-7，而其他形式的Kalirin则在细胞体和整个神经突中可见。当在成纤维细胞中瞬时表达时，Kalirin-7及其Dbl同源-普列克底物蛋白同源结构域可诱导片状伪足和膜皱褶的形成，这表明Rac1被激活。利用Rac1，Dbl同源-普列克底物蛋白同源结构域催化了结合的GDP与GTP的体外交换。Kalirin-7是在突触后致密部分中鉴定出的第一个鸟嘌呤核苷酸交换因子，它在该位置处于最佳位置，可调节连接膜蛋白和肌动蛋白细胞骨架的信号转导途径。
