Human Periostin/OSF‑2 Biotinylated Antibody

Human OSF-2 (osteoblast-specific factor 2; also periostin) is a 170 kDa secreted homodimeric protein that belongs to the periostin family of the FAS1 superfamily of molecules (1-4). It is a TGF-beta inducible molecule that serves as both an adhesion molecule and tumor suppressor (2, 5, 6, 7). It is synthesized as an 836 amino acid (aa) precursor that contains a 21 aa signal sequence and an 815 aa mature region (2, 8). It is unknown if the molecule has any significant glycosylation (2). The human homodimer is not disulfide-linked (3). The molecule consists of two distinct regions. The N-terminus contains an 55 aa EMI domain, while the C-terminus contains four 130 aa fasciculin type 1 (FAS1) domains. The EMI domain is cysteine-rich and shows a highly basic alpha-helix (9). Each FAS1 repeat exhibits a novel seven-stranded beta‑wedge with a multiple alpha-helical fold (1, 8). Three alternate splice forms are known that are C-terminal to the fourfold FAS1 repeats. These mature molecules are 758 and 761 aa in length. The first shows a one aa substitution for aa 649-706 of the mature molecule. The second shows a one aa substitution for aa 649-676, and a deletion of 27 aa between aa 784-810 of the mature molecule (10). The significance of the alternate splice forms is not clear. OSF-2 is known to bind to alpha_v beta₃ and alpha_v beta₅ integrins (3). It is synthesized by smooth muscle cells, fibroblasts, osteoblasts, and multiple carcinoma cell types (2, 3, 5, 7, 11, 12). OSF-2 induces expression of VEGFR2/KDR on endothelial cells (EC) by binding to EC alpha_v beta₃ (12). It also promotes cell transformation to a tumorigenic phenotype, accompanied by MMP-9 and fibronectin production and cell migration (13). Mature human OSF-2 is 91%, 96% and 91% aa identical to rat, dog, and mouse OSF-2, respectively.