|complement factor D (adipsin)|
Factor D in Homo sapiens 
|Alt. symbols||DF, PFD|
|Locus||Chr. 19 p13.3|
Factor D (EC 18.104.22.168, C3 proactivator convertase, properdin factor D esterase, factor D (complement), complement factor D, CFD, adipsin) a protein which in humans is encoded by the CFD gene. Factor D is involved in the alternative complement pathway of the complement system where it cleaves factor B.
The protein encoded by this gene is a member of the trypsin family of peptidases. The encoded protein is a component of the alternative complement pathway best known for its role in humoral suppression of infectious agents. This protein is also a serine protease that is secreted by adipocytes into the bloodstream. Finally, the encoded protein has a high level of expression in fat, suggesting a role for adipose tissue in immune system biology.
The level of Factor D is elevated in the obese, this elevation may be due to high activity or resistance but exact cause is not totally known.
All members of the chymotrypsin family of serine proteases have very similar structures. In all cases, including factor D, there are two antiparallel β-barrel domains with each barrel containing six β-strands with the same typology in all enzymes. The major difference in backbone structure between Factor D and the other serine proteases of the chymotrpsin family is in the surface loops connecting the secondary structural elements. Factor D displays different conformations of major catalytic and substrate-binding residues typically found in the chrotrypsin family. These features suggest the catalytic activity of factor D is prohibited unless conformational changes are induced by a realignment.
- PDB 1HFD; Narayana SV, Carson M, el-Kabbani O, et al. (January 1994). "Structure of human factor D. A complement system protein at 2.0 A resolution". J. Mol. Biol. 235 (2): 695–708. doi:10.1006/jmbi.1994.1021. PMID 8289289.
- "Entrez Gene: CFD".
- Ronti T, Lupattelli G, Mannarino E (April 2006). "The endocrine function of adipose tissue: an update". Clin. Endocrinol. (Oxf) 64 (4): 355–65. doi:10.1111/j.1365-2265.2006.02474.x. PMID 16584505. Lay summary – medscape.com.
- Volanakis JE, Narayana SV (April 1996). "Complement factor D, a novel serine protease". Protein Sci. 5 (4): 553–64. doi:10.1002/pro.5560050401. PMC 2143395. PMID 8845746.