Recombinant Human SMOC-1 Protein, CF

SMOC-1 (secreted, or SPARC-related, modular calcium-binding protein 1) is a 70 - 90 kDa secreted glycoprotein that is a member of the SPARC family of matricellular molecules (1). Mature human SMOC-1 is 408 amino acids (aa) in length. It contains one Kazal-like domain (aa 42 - 87), two thyroglobulin type-1 (TY) segments (aa 92 - 159 and 224 - 292) and two EF-hand sequences (aa 359 - 394 and 396 - 431). One potential splice variant contains a 16 aa region of alternate sequence between the TY domains, a 7 aa deletion between the TY and EF-hand domains, and three alternate aa at the C-terminus. Mature human SMOC-1 shares 92% aa identity with mouse and rat SMOC-1 and 97%, 96% and 95% aa identity with canine, bovine and porcine SMOC-1, respectively. The principal difference between rodents and other mammals is an additional 19 aa near the C-terminus of rodent SMOC-1. Like other matricellular proteins, SMOC-1 is primarily expressed in basement membranes, although it has also been found in other extracellular matrices and the oocyte zona pellucida (1). It is present early in mouse embryogenesis, and is produced by cells deriving from all three germ layers (4). Recombinant bacterially produced human SMOC-1 and SMOC-2 were both shown to bind the acute phase protein, C-reactive protein, and the adhesion proteins, fibulin and vitronectin (2). A signaling role for SMOC-1 was shown in rat mesangial cells: induction of nitric oxide in response to inflammatory cytokines downregulates SMOC-1 which, in turn, downregulates expression of TGF-beta and TGF-beta -regulated genes. This mechanism is proposed to limit the profibrotic effects of TGF-beta, for example in the glomerulus (5). In Xenopus, the SMOC paralog has been shown to antagonize BMP activity.