Bioinformatics as a Starting Point for the Analysis of ALK1 Missense Mutations

Background: Activin A receptor, type II-like kinase 1 (also called ALK1), is a serine-threonine kinase predominantly expressed on endothelial cell surface, involved in TGF-β signalling. It is encoded by the ACVRL1 gene (12q11-14), whose mutations cause type 2 Hereditary Hemorrhagic Telangiectasia (HHT2), an autosomal dominant multisystem vascular dysplasia. Although an X-ray structure of ALK1 intracellular domain has recently become available (PDB ID: 3MY0), structure determination of ALK1 ectodomain (ALK1EC) has been elusive so far. Methods: We recently described the building of a homology model for ALK1EC, followed by an extensive bioinformatic analysis, based on a set of 38 methods, of the effect of missense mutations at the sequence and structural level. ALK1EC potential interaction with its ligand BMP9 was then predicted combining modelling and docking data. Results: Major structural changes and loss of stability of the protein were predicted for several mutations, whereas others were found to interfere mainly with binding to BMP9 or other interactors, like Endoglin (CD105), whose encoding ENG gene (9q34) mutations are known to cause type 1 HHT. Conclusions: Building on these predictions, we are now creating a library with the most interesting mutations, both by gene synthesis and site-directed mutagenesis, to try to express them and analyse their effects on endothelial cells by in vitro and in vivo tests, as well as to determine the real crystal structures.