The cryoEM Structure of mTLD Reveals a Potential Molecular Basis for Dimerisation and Substrate Exclusion

Abstract

The extracellular matrix (ECM) makes up 80% of our body, playing an important role in cell proliferation, migration, and development. While proteins such as bone morphogenic proteins (BMPs) regulate complex cell signalling events, proteins such as collagen and fibronectin provide the substrate to which cells adhere. Collagens undergo complex assembly and maturation processes that are not yet fully understood. During maturation, procollagen chains form heteromers, which are secreted into the extracellular matrix and undergo proteolytic maturation by different types of proteases. mTLD is a member of the BMP1/tolloid-like proteinase family (BTPs), which processes procollagen and regulates bone morphogenic protein signalling pathways through the cleavage of the BMP antagonist chordin. Dysregulation of these processes is known to result in diseases, including Osteogenesis imperfecta and Ullrich congenital muscular dystrophy. Whilst lower-resolution structures of mTLD and crystal structures of its individual domains have provided insights into its function, high-resolution analysis of full-length mTLD and its interactions with substrates is required to establish the structure-function relationship between BTPs and their substrates. These will also provide the molecular context of disease-associated mutations and their respective pathomechanisms. Beyond the role of BTPs, the molecular basis of collagen assembly is not yet fully understood due to the complexity of the maturation process. Whilst low-resolution structures have provided insights into the architecture of collagen fibres and microfibrils, model systems are required to better study the structural basis of chain recognition and assembly to establish the structure-function relationship of disease-associated mutations. This study presents a high-resolution structure of full-length dimeric mTLD, providing insights into the molecular basis of dimerisation and BTP-substrate interactions. Additionally, we present a novel model system to study collagen IV, a microfibrillar collagen involved in forming cell adhesions and regulating cell proliferation. We show that this model system is amenable to high-resolution structural analysis, providing a novel tool to study the molecular basis of collagen VI maturation and the pathomechanisms of disease-associated mutations. Overall, these findings will help us understand the molecular and biochemical basis of the formation and regulation of the extracellular matrix and cell-matrix interactions.

Date of Award	1 Jan 1824
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Clair Baldock (Supervisor)