Structure and function of ADAMTSL proteins and their role in tissue organisation

Elastic tissues such as eye ligaments, skin, blood vessels and lung contain elastic fibres which are composed of elastin and fibrillin microfibrils. Mutations in elastic fibres disrupt the overall function of these tissues and result in a wide spectrum of diseases. Collectively they are termed fibrillinopathies as they are usually caused by mutations in fibrillin. However recently, mutations in a family of matrix metalloproteases termed A Disintegrin And Metalloprotease with Thrombospondin type 1 repeats (ADAMTS) and ADAMTS-like (ADAMTS-L) proteins have been found to give rise to the same diseases. For instance, mutations in ADAMTSL4 give rise to ectopia lentis (EL) or dislocated lenses, mutations in ADAMTSL-2 to Geleophysic Dysplasia and mutations in ADAMTS10 to Weill-Marchesani Syndrome.

The ADAMTS family is composed of multi-domain zinc metalloproteases with a number of non-catalytic ancillary domains. The ADAMTSL proteins are composed of the ancillary domains but lack the catalytic domain and activity. ADAMTS-L4 co-localises to fibrillin microfibrils in the anterior chamber of the eye including the ciliary zonules, which is consistent with its role in tethering the lens to the ciliary body. An ADAMTSL-4 mutant mouse has disordered fibrillin microfibrils indicating a role for ADAMTS-L4 in microfibril deposition (Collin et al., 2014). However, little is known about the structure of ADAMTSL proteins, the interactions they makes with elastic fibre proteins or their function in the matrix.

Therefore the aims of this project are:
1) To investigate the interactions between ADAMTSL proteins, fibrillin and other elastic fibre proteins using binding assays such as Surface Plasmon Resonance and micro-isothermal titration calorimetry. The consequence of ADAMTSL disease-causing mutations on protein interactions and signalling will be investigated using biochemical and cell-based approaches.
2) To determine the structure of a member of the ADAMTSL family and an ADAMTSL-fibrillin complex using cryoEM and single particle analysis.
3) To define the organisation of ADAMTSL-4 in ocular tissue such as the ciliary zonules using immunohistochemistry and serial blockface SEM imaging and to compare with the organization of the ciliary zonules in the ADAMTSL-4 mutant mouse.

Underpinning these approaches are advanced imaging techniques including cryo-EM and 3D reconstruction, and serial blockface SEM imaging. Combining these interdisciplinary approaches from molecular structure to whole tissue function will allow us to understand the role of ADAMTSL proteins in fibrillin assembly and the consequence of ADAMTSL-4 mutations on eye disease.