Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Hong Kong, China.
State Key Laboratory of Genetic Engineering, School of Life Sciences, Fudan University, Shanghai, China.
J Cell Biol. 2022 Aug 1;221(8). doi: 10.1083/jcb.202105035. Epub 2022 Jul 12.
IRSp53 (aka BAIAP2) is a scaffold protein that couples membranes with the cytoskeleton in actin-filled protrusions such as filopodia and lamellipodia. The protein is abundantly expressed in excitatory synapses and is essential for synapse development and synaptic plasticity, although with poorly understood mechanisms. Here we show that specific multivalent interactions between IRSp53 and its binding partners PSD-95 or Shank3 drive phase separation of the complexes in solution. IRSp53 can be enriched to the reconstituted excitatory PSD (ePSD) condensates via bridging to the core and deeper layers of ePSD. Overexpression of a mutant defective in the IRSp53/PSD-95 interaction perturbs synaptic enrichment of IRSp53 in mouse cortical neurons. The reconstituted PSD condensates promote bundled actin filament formation both in solution and on membranes, via IRSp53-mediated actin binding and bundling. Overexpression of mutants that perturb IRSp53-actin interaction leads to defects in synaptic maturation of cortical neurons. Together, our studies provide potential mechanistic insights into the physiological roles of IRSp53 in synapse formation and function.
IRSp53（又名 BAIAP2）是一种支架蛋白，可将膜与肌动蛋白填充的突起（如丝状伪足和片状伪足）中的细胞骨架连接起来。该蛋白在兴奋性突触中大量表达，对于突触发育和突触可塑性至关重要，但其机制尚不清楚。本文作者表明，IRSp53 与其结合伴侣 PSD-95 或 Shank3 之间的特定多价相互作用驱动了复合物在溶液中的相分离。IRSp53 可以通过桥接到 ePSD 的核心和更深层，被富集到再构建的兴奋性突触后致密区（ePSD）凝聚物中。IRSp53/PSD-95 相互作用缺陷的突变体的过表达会扰乱小鼠皮质神经元中 IRSp53 的突触富集。再构建的 PSD 凝聚物通过 IRSp53 介导的肌动蛋白结合和成束作用，促进溶液中和膜上束状肌动蛋白丝的形成。扰乱 IRSp53-肌动蛋白相互作用的突变体的过表达会导致皮质神经元突触成熟缺陷。总之，这些研究为 IRSp53 在突触形成和功能中的生理作用提供了潜在的机制见解。
