Factor D

The protein encoded by this gene is a member of the trypsin family of serine proteases secreted by adipocytes into the bloodstream.

The encoded protein is a component of the alternative complement pathway best known for its role in humoral suppression of infectious agents.

Finally, the encoded protein has a high level of expression in fat, suggesting a role for adipose tissue in immune system biology.

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

Factor D displays different conformations of major catalytic and substrate-binding residues typically found in the chrotrypsin family.

Other key components of Factor D are an Asp189-Arg218 salt bridge that stabilizes a self-inhibitory loop (amino acid residues 212 to 218) and His57 side chain in the non-canonical conformation.

The mode of inheritance of Factor D deficiency is autosomal recessive, and individuals with a mutation on only one allele may not experience the same susceptibility to reoccurring infections.

Alternative pathway. ( 4. Is factor D cleaving B to Bb and Ba)
The non-canonical conformation of Factor D is inhibited by the self-inhibitory loop (blue). The Asp-Arg salt bridge (purple and orange side chains, respectively) stabilizes the self-inhibitory loop. The catalytic triad is shown in green. [ 13 ]
The canonical conformation of Factor D is not self-inhibited. The Asp-Arg salt bridge (purple and orange side chains, respectively) has been displaced resulting in a shift in the self inhibitory loop (blue). The catalytic triad is shown in green. [ 14 ]