Microfibril-associated glycoprotein-2 interacts with fibrillin-1 and fibrillin-2 suggesting a role for MAGP-2 in elastic fiber assembly

Elastic fibers are composed of the protein elastin and a network of 10-12 nm microfibrils. The microfibrillar proteins include, among others, the fibrillins and microfibril-associated glycoproteins-1 and -2 (MAGP-1 and MAGP-2). Little is known about how microfibrillar proteins interact to support fiber assembly. We used the C-terminal half of MAGP-2 in a yeast two-hybrid library screen to identify relevant ligands. Six of 13 positive clones encoded known microfibrillar proteins, including fibrillin-1 and -2. Deletion analysis of partial fibrillin-1 and -2 clones revealed a calcium-binding epidermal growth factor repeat-containing region near the C terminus responsible for binding. This region is distinct from the region of fibrillin-1 reported by others to bind MAGP-1. The MAGP-2 bait was unable to interact productively with other epidermal growth factor repeats in fibrillin-1, demonstrating specificity of the interaction. Deletion analysis of the MAGP-2 bait demonstrated that binding occurred in a core region containing 48% identity and 7 conserved cysteine residues with MAGP-1. Immunoprecipitation of MAGP-2 from transfected COS-7 cells resulted in the coprecipitation of fibrillin. These results demonstrate that MAGP-2 specifically interacts with fibrillin-1 and -2 and suggest that MAGP-2 may help regulate microfibrillar assembly. The results also demonstrate the utility of the yeast two-hybrid system to study protein-protein interactions of the extracellular matrix.