A weakened interface in the P182L variant of HSP27 associated with severe Charcot‐Marie‐Tooth neuropathy causes aberrant binding to interacting proteins

HSP27 is a human molecular chaperone that forms large, dynamic oligomers and functions in many aspects of cellular homeostasis. Mutations in HSP27 cause Charcot‐Marie‐Tooth (CMT) disease, the most common inherited disorder of the peripheral nervous system. A particularly severe form of CMT disease is triggered by the P182L mutation in the highly conserved IxI/V motif of the disordered C‐terminal region, which interacts weakly with the structured core domain of HSP27. Here, we observed that the P182L mutation disrupts the chaperone activity and significantly increases the size of HSP27 oligomers formed in vivo, including in motor neurons differentiated from CMT patient‐derived stem cells. Using NMR spectroscopy, we determined that the P182L mutation decreases the affinity of the HSP27 IxI/V motif for its own core domain, leaving this binding site more accessible for other IxI/V‐containing proteins. We identified multiple IxI/V‐bearing proteins that bind with higher affinity to the P182L variant due to the increased availability of the IxI/V‐binding site. Our results provide a mechanistic basis for the impact of the P182L mutation on HSP27 and suggest that the IxI/V motif plays an important, regulatory role in modulating protein–protein interactions.     

Immunoreactivity for S-100 protein in dendritic and in lymphocyte-like cells in human lymphoid tissues

S-100 protein is an immunohistochemical marker for a subset of dendritic cells, the interdigitating reticulum cells (IDRCs), which are mainly located in T-dependent areas of lymphoid tissues. In the present study we have investigated the distribution of S-100-positive cells in lymph nodes, spleen, thymus and peripheral blood of normal subjects. Immunoreactivity for S-100 protein was demonstrated in large cells with dendritic morphology and in small lymphocyte-like cells present in the lymph node paracortex, thymic medulla, splenic periarterial lymphatic sheaths (PALS) and in peripheral blood. S-100-positive lymphocyte-like cells were frequently detected around high endothelial venules (HEV) and were present in numbers comparable to those of S-100-positive IDRCs. Immunoelectron microscopy confirmed the existence of positive cells with lymphoid morphology and revealed that the intracellular distribution of the immunoreaction product was similar in lymphoid and dendritic cells. Further characterization of S-100-positive cells demonstrated that both lymphoid and dendritic cells were unreactive with a large panel of monocytic and macrophage markers.