NMR structure and functional studies of the fourth FAS1 domain of human periostin

Periostin is a matricellular protein that consists of several structural and functional domains, including EMILIN-like, four internal repeat fasciclin1 (FAS1) domains, and a carboxyl-terminal variable domain. It is known that periostin is associated with various fundamental biological processes and diseases, such as several types of cancer and chronic inflammatory diseases. Despite its important roles, the biological function of each domain is poorly understood. In this study, we expressed the fourth FAS1 (FAS1 IV) domain of human periostin, which was highly soluble and stable enough for structural and functional studies. The three-dimensional structure of FAS1 IV was determined using 3D NMR spectroscopy. The overall structure of FAS1 IV consists of six α-helices, one 310 helix, and eight β-strands. Two triangular α-helical modules formed by three α-helices each are located on one side of the molecule, while the orthogonal β-sheet sandwich module of FAS1 IV is located on the other side. The isolated FAS1 IV domain exhibited cell invasion, migration, and adhesion activities for cancer cell lines comparable to those of the full FAS1 I–IV domain. In conclusion, we propose that the FAS1 IV domain is functionally active in human periostin and provides valuable information for understanding the biological function of periostin.