Abstract
VAPB (Vesicle-Associated-membrane Protein-associated protein B) is a tail-anchored membrane protein of the endoplasmic reticulum that can also be detected at the inner nuclear membrane. As a component of many contact sites between the endoplasmic reticulum and other organelles, VAPB is engaged in multiple protein interactions with a plethora of binding partners. A mutant version of VAPB, P56S-VAPB, which results from a single point mutation, is involved in a familial form of amyotrophic lateral sclerosis (ALS8). We performed RAPIDS (rapamycin- and APEX-dependent identification of proteins by SILAC) to identify proteins that interact with or are in close proximity to P56S-VAPB. The mutation abrogates the interaction of VAPB with many known binding partners. Here, we identify Sequestosome 1 (SQSTM1), a well-known autophagic adapter protein, as a major interaction/proximity partner of P56S-VAPB. Remarkably, not only the mutant protein, but also wild-type VAPB interacts with SQSTM1, as shown by proximity ligation assays and co-immunoprecipiation experiments.
Highlights
The Vesicle-Associated-membrane Protein-associated protein B (VAPB) is a member of a small protein family that contains VAPA and the MOtile SPerm Domain- containing proteins 1, 2 and 3 (MOSPD1, MOSPD2 and MOSPD3) [1,2]
A very clear effect was observed for the RNA-binding protein TIA1, which accumulated inside the nucleus in control cells or in cells expressing wild type HA-VAPB, but co-localized with HA-P56S-VAPB in cytoplasmic aggregates of transfected cells
We did not detect the recruitment of FUS or TDP-43 to the cytoplasmic aggregates, in contrast to a previous publication [36] and no colocalization with autophagosome or lysosome membrane proteins, LC3 and LAMP1 was observed in our study (Figure S1)
Summary
The Vesicle-Associated-membrane Protein-associated protein B (VAPB) is a member of a small protein family that contains VAPA and the MOtile SPerm Domain- containing proteins 1, 2 and 3 (MOSPD1, MOSPD2 and MOSPD3) [1,2]. These proteins share a Major Sperm Protein (MSP) domain that is involved in protein–protein interactions. Structures of the entire VAPB protein, according to an AlphaFold prediction [14] and of the MSP-domain of VAPB [15], are shown in Figure 1A,B, respectively
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