Factor D

Factor D also known as complement factor D(CFD) or 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.

Function
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.



Factor D is a serine protease that stimulates glucose transport for triglyceride accumulation in fats cells and inhibits lipolysis.

Clinical significance
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.

Structure
All members of the chymotrypsin family of serine proteases have very similar structures. In all cases, including factor D, there is 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.