Surfactant Protein D (SFTPD) (AA 21-375) protein (His tag)
Description
Surfactant Pulmonary-Associated Protein D (SP-D) is a 43 kDa member of the collectin family of innate immune modulators. Its principal components consist of a collagen-like region and a C-terminal carbohydrate recognition domain (CRD), a structure that places it in a subset of pattern recognition proteins termed defense collagens. SP-D is constitutively secreted by alveolar lining cells and epithelium associated with tubular structures and induced in cardiac smooth muscle and endothelial cells. It binds both secreted and transmembrane proteins that transduce its function. It binds human neutrophil defensins, modulating influenza anti-viral defense. It binds MD-2/LY96, a secreted protein that cooperates with Toll-like receptors (TLRs) in the response of macrophages to bacterial lipopolysaccharides (LPS) or cell wall components. It also binds macrophage CD14 and TLRs directly, blocking binding of LPS and down-regulating TNF-alpha secretion. SP-D binding of both SIRPalpha and the calreticulin/CD91 complex on macrophages allows for a graded response to environmental challenge via the following mechanism: when the ratio of antigen/pathogen to available CRDs is low, antigen can be bound without occupying all available CRDs. The free CRDs will bind to SIRPalpha, generating a signal that downmodulates the inflammatory response. When virtually all CRDs are occupied by ligand, however, free CRDs are not available for SIRPalpha binding. Instead, the dodecamer is thought to rearrange, exposing the N-termini of all four linked trimers which bind to the calreticulin/CD91 complex and initiate inflammation. Thus, SP-D provides a mechanism for the clearance of small antigenic insults without the need for a damaging inflammatory response.Alternative Names: Pulmonary Surfactant-Associated Protein D, PSP-D, SP-D, Collectin-7, Lung Surfactant Protein D, SFTPD, COLEC7, PSPD, SFTP4