Liao Zhitao, Jia Bowen, Guan Dongshi, Chen Xudong, Zhang Mingjie, Tong Penger
Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
Division of Life Science, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
Nat Commun. 2025 Jun 5;16(1):5237. doi: 10.1038/s41467-025-60345-9.
Multivalent proteins can form membraneless condensates in cells by liquid-liquid phase separation, and significant efforts have been made to study their biochemical properties. Here, we demonstrate the emergent mechanics of a functional multivalent condensate reconstituted with six postsynaptic density proteins, using atomic-force-microscopy-based mesoscale rheology and quantitative fluorescence measurements. The measured relaxation modulus and protein mobility reveal that the majority (80%) of the proteins in the condensate are mobile and diffuse through a dynamically cross-linked network made of the remaining (20%) non-mobile scaffold proteins. This percolating structure gives rise to a two-mode mechanical relaxation with an initial exponential decay followed by a long-time power-law decay, which differs significantly from simple Maxwell fluids. The power-law rheology with an exponent α ≃ 0.5 is a hallmark of weak bonds' binding/unbinding dynamics in the multivalent protein network. The concurrent molecular and mechanical profiling thus provides a reliable readout for characterizing the mechanical state of protein condensates and investigating their physiological functions and associations with diseases.
多价蛋白可通过液-液相分离在细胞中形成无膜凝聚物，并且人们已付出巨大努力来研究它们的生化特性。在此，我们利用基于原子力显微镜的中尺度流变学和定量荧光测量，展示了由六种突触后致密蛋白重构的功能性多价凝聚物的新兴力学特性。所测得的弛豫模量和蛋白质迁移率表明，凝聚物中大多数（80%）蛋白质是可移动的，并通过由其余（20%）不可移动的支架蛋白构成的动态交联网络扩散。这种渗流结构产生了一种双模式机械弛豫，先是初始指数衰减，随后是长时间幂律衰减，这与简单麦克斯韦流体有显著差异。指数α≃0.5的幂律流变学是多价蛋白质网络中弱键结合/解离动力学的一个标志。因此，同时进行的分子和力学分析为表征蛋白质凝聚物的力学状态以及研究它们的生理功能和与疾病的关联提供了可靠的读数。
