Biology subjects

Mortensen, S. A.

Publications and source records attributed to Mortensen, S. A..

5 recordsLinked to original sources

bioRxiv2023

Amino acid substitutions hydrophilizing the core of titin domains cause dilated cardiomyopathy

The underlying genetic defect in most cases of dilated cardiomyopathy (DCM), a common inherited heart disease, remains unknown. Intriguingly, many patients carry single missense variants of uncertain pathogenicity targeting the giant protein titin, a fundamental sarcomere component. To explore the deleterious potential of these variants, we first solved the wild-type and mutant crystal structures of I21, the titin domain targeted by pathogenic variant p.C3575S. Although both structures are remarkably similar, the increase in hydrophilicity of deeply buried position 3575 strongly destabilizes the mutant domain, a scenario supported by molecular dynamics simulations and by biochemical assays that show no disulfide involving C3575. Prompted by these observations, we have found that thousands of similar hydrophilizing variants associate specifically with DCM. Hence, our results imply that titin domain destabilization causes DCM, a conceptual framework that not only informs pathogenicity assessment of gene variants but also points to therapeutic strategies counterbalancing protein destabilization.

biochemistry↗

bioRxiv2023

Structure of the N-terminal didomain d1_d2 of the Thrombospondin type-1 domain-containing 7A

Thrombospondin type-1 domain-containing 7A (THSD7A) is a large extracellular protein that is found in podocyte foot processes of the kidney glomerulus. It has been established as a causative autoantigen in membranous nephropathy. Amongst the predicted 21 thrombospondin repeat domains of its extracellular segment, the highest frequency of autoimmune response has been associated with the two N-terminal domains. Here, we show that antibodies against this THSD7A segment in mice induce typical clinical and morphological signs of membranous nephropathy. The high-resolution structure of these two domains reveals a non-canonical thrombospondin repeat fold that is distinct from the established type 1 thrombospondin repeat. As it shares a conserved disulfide pattern with the canonical fold, we refer to these domains d1 and d2 as type 1A thrombospondin repeats. Both domains comprise a seven layered CC-W-PP-R-W-QQ-CC pattern, which is only partly shared by other THSD7A thrombospondin repeat domains. The two domains form a well-defined V-shaped tandem arrangement. Our findings provide crucial insight into specific structural features of these two domains that are distinct from other regions of THSD7A and hence could cause the high level of antigenicity found for these two domains.

biophysics↗

bioRxiv2022

Structure-based discovery of a non-canonical prototype long-chain monoacylglycerol lipase through an endogenous catalysis intermediate complex

The identification and characterization of enzyme function is largely lacking behind the rapidly increasing availability of large numbers of sequences and associated high-resolution structures. This is often hampered by lack of knowledge on in vivo relevant substrates. Here, we present a case study of a high-resolution structure of an unusual orphan lipase in complex with an endogenous C18 monoacylglycerol ester reaction intermediate from the expression host, which is insoluble under aqueous conditions and thus not accessible for studies in solution. The data allowed its functional characterization as a prototypic long-chain monoacylglycerol lipase, which uses a minimal lid domain to position the substrate through a hydrophobic tunnel directly to the enzymes active site. Knowledge about the molecular details of the substrate binding site allowed us to modulate the enzymatic activity by adjusting protein/substrate interactions, demonstrating the potential of our findings for future biotechnology applications.

biochemistry↗

bioRxiv2020

Structure of the mycobacterial ESX-5 Type VII Secretion System hexameric pore complex

To establish an infection, pathogenic mycobacteria use the Type VII secretion or ESX system to secrete virulence proteins across their cell envelope. The five ESX systems (ESX-1 to ESX-5) have evolved diverse functions in the cell, with the ESX-5 found almost exclusively in pathogens. Here we present a high-resolution cryo-electron microscopy structure of the hexameric ESX-5 Type VII secretion system. This 2.1 MDa membrane protein complex is built by a total of 30 subunits from six protomeric units, which are composed of the core components EccB5, EccC5, two copies of EccD5, and EccE5. The hexameric assembly of the overall ESX-5 complex is defined by specific inter-protomer interactions mediated by EccB5 and EccC5. The central transmembrane pore is formed by six pairs of EccC5 transmembrane helices that adopt a closed conformation in the absence of substrate in our structure. On the periplasmic face of the ESX-5 complex, we observe an extended arrangement of the six EccB5 subunits around a central cleft. Our structural findings provide molecular details of ESX-5 assembly and observations of the central secretion pore, which reveal insights into possible gating mechanisms used to regulate the transport of substrates.

microbiology↗

bioRxiv2019

Structural basis of p62/SQSTM1 helical filaments, their presence in p62 bodies and role in cargo recognition in the cell

p62/SQSTM1 is an autophagy receptor and signaling adaptor with an N-terminal PB1 domain that forms the scaffold of phase-separated p62 bodies in the cell. The molecular determinants that govern PB1 domain filament formation in vitro remain to be determined and the role of p62 filaments inside the cell is currently unclear. We determined four high-resolution cryo-EM structures of different human and Arabidopsis PB1 domain assemblies and observed a filamentous ultrastructure of phase-separated p62/SQSTM1 bodies using correlative cellular EM. We show that oligomerization or polymerization, driven by a double arginine finger in the PB1 domain, is a general requirement for lysosomal targeting of p62. Furthermore, the filamentous assembly state of p62 is required for autophagosomal processing of the p62-specific cargo KEAP1. Our results show that using such mechanisms, p62 filaments can be critical for cargo recognition and are an integral part of phase separated p62 bodies.

molecular biology↗