Biology subjects

Timmerman, V.

Publications and source records attributed to Timmerman, V..

3 recordsLinked to original sources

bioRxiv2019

BAG3 Pro209 mutants associated with myopathy and neuropathy sequester chaperones of the CASA-complex in aggresomes

Three missense mutations targeting the same proline 209 (Pro209) codon in the co-chaperone Bcl2-associated athanogene 3 (BAG3) have been reported to cause distal myopathy, dilated cardiomyopathy or Charcot-Marie-Tooth type 2 neuropathy. Yet, it is unclear whether distinct molecular mechanisms underlie the variable clinical spectrum of the rare patients carrying these three heterozygous Pro209 mutations in BAG3. Here, we studied all three variants and compared them to the BAG3_Glu455Lys mutant, which causes dilated cardiomyopathy. We found that all BAG3_Pro209 mutants have acquired a toxic gain-of-function, which causes these variants to accumulate in the form of insoluble HDAC6- and vimentin-positive aggresomes. The aggresomes formed by mutant BAG3 led to a relocation of other chaperones such as HSPB8 and Hsp70, which, together with BAG3, promote the so-called chaperone-assisted selective autophagy (CASA). As a consequence of their increased aggregation-proneness, mutant BAG3 trapped ubiquitinylated client proteins at the aggresome, preventing their efficient clearance. Combined, these data show that all BAG3_Pro209 mutants, irrespective of their different clinical phenotypes, are characterized by a gain-of-function that contributes to the gradual loss of protein homeostasis.

cell biology↗

bioRxiv2019

Dysregulation of HSP27 oligomerization and interactions by a neuropathy-causing mutation in the C-terminal IPV motif

HSP27 (HSPB1) is a systemically expressed human small heat-shock protein that forms large, dynamic oligomers and functions in various aspects of cellular homeostasis. Mutations in HSP27 cause Charcot-Marie-Tooth disease, the most common inherited disorder of the peripheral nervous system. A particularly severe form of the disease is triggered by the P182L mutation within the highly conserved IxI/V motif of HSP27. Here, we observed that the P182L variant of HSP27 lacks the ability to prevent the aggregation of client proteins and formed significantly larger oligomers both in vitro and in vivo. NMR spectroscopy revealed that the P182L IxI/V motif binds its -crystallin domain with significantly lower association rate, and thus affinity, rendering the binding site more available for other interactors. We identified 22 IxI/V-containing proteins that are known to interact with HSP27 and could therefore bind with enhanced affinity to the P182L variant. We validated this hypothesis through co-immunoprecipitation experiments, revealing that the IxI/V motif-bearing co-chaperone BAG3 indeed binds with higher affinity to the P182L variant. Our results provide a mechanistic basis for the impact of the P182L mutation on HSP27, and highlight the general importance of the IxI/V motif and its role in protein-protein interaction networks.

biochemistry↗

bioRxiv2017

Sensory neuropathy-causing mutations in ATL3 cause aberrant ER membrane tethering

The ER is a complex network of sheets and tubules that is continuously being remodeled. The relevance of this membrane dynamics is underscored by the fact that mutations in Atlastins (ATL), the ER fusion proteins in mammals, cause neurodegeneration. How defects in this process disrupt neuronal homeostasis is largely unknown. Here we show by EM volume reconstruction of transfected cells, neurons and patient fibroblasts that the HSAN-causing ATL3 mutants promote aberrant ER tethering hallmarked by bundles of laterally attached ER tubules. In vitro, these mutants cause excessive liposome tethering, recapitulating the results in cells. Moreover, ATL3 variants retain their dimerization-dependent GTPase activity, but are unable to promote membrane fusion, suggesting a defect on an intermediate step of the ATL3 functional cycle. Our data therefore show that the effects of ATL3 mutations on ER network organization stretch beyond a loss of fusion, shedding a new light on neuropathies caused by atlastin defects.

cell biology↗