Comoletti Davide, Flynn Robyn E, Boucard Antony A, Demeler Borries, Schirf Virgil, Shi Jianxin, Jennings Lori L, Newlin Helen R, Südhof Thomas C, Taylor Palmer
Department of Pharmacology, University of California-San Diego, La Jolla, California 92093-0636, USA.
Biochemistry. 2006 Oct 24;45(42):12816-27. doi: 10.1021/bi0614131.
Neuroligins 1-4 are postsynaptic transmembrane proteins capable of initiating presynaptic maturation via interactions with beta-neurexin. Both neuroligins and beta-neurexins have alternatively spliced inserts in their extracellular domains. Using analytical ultracentrifugation, we determined that the extracellular domains of the neuroligins sediment as dimers, whereas the extracellular domains of the beta-neurexins appear monomeric. Sedimentation velocity experiments of titrated stoichiometry ratios of beta-neurexin and neuroligin suggested a 2:2 complex formation. The recognition properties of individual neuroligins toward beta-neurexin-1 (NX1beta), along with the influence of their splice inserts, were explored by surface plasmon resonance and affinity chromatography. Different neuroligins display a range of NX1beta affinities spanning more than 2 orders of magnitude. Whereas splice insert 4 in beta-neurexin appears to act only as a modulator of the neuroligin/beta-neurexin association, splice insert B in neuroligin-1 (NL1) is the key element regulating the NL1/NX1beta binding. Our data indicate that gene selection, mRNA splicing, and post-translational modifications combine to give rise to a controlled neuroligin recognition code with a rank ordering of affinities for particular neurexins that is conserved for the neuroligins across mammalian species.
神经连接蛋白1 - 4是突触后跨膜蛋白，能够通过与β-神经素相互作用引发突触前成熟。神经连接蛋白和β-神经素在其细胞外结构域都有可变剪接插入片段。使用分析型超速离心法，我们确定神经连接蛋白的细胞外结构域以二聚体形式沉降，而β-神经素的细胞外结构域呈单体形式。β-神经素与神经连接蛋白滴定化学计量比的沉降速度实验表明形成了2:2复合物。通过表面等离子体共振和亲和色谱法研究了各个神经连接蛋白对β-神经素-1（NX1β）的识别特性及其剪接插入片段的影响。不同的神经连接蛋白对NX1β的亲和力范围跨越超过2个数量级。虽然β-神经素中的剪接插入片段4似乎仅作为神经连接蛋白/β-神经素结合的调节剂，但神经连接蛋白-1（NL1）中的剪接插入片段B是调节NL1/NX1β结合的关键元件。我们的数据表明，基因选择、mRNA剪接和翻译后修饰共同产生了一个受控的神经连接蛋白识别密码，对特定神经素的亲和力具有等级排序，这在整个哺乳动物物种的神经连接蛋白中是保守的。
