This gene encodes a member of the S1， or chymotrypsin， family of serine peptidases. This protease catalyzes the cleavage of factor B， the rate-limiting step of the alternative pathway of complement activation. This protein also functions as an adipokine， a cell signaling protein secreted by adipocytes， which regulates insulin secretion in mice. Mutations in this gene underlie complement factor D deficiency， which is associated with recurrent bacterial meningitis infections in human patients. Alternative splicing of this gene results in multiple transcript variants. At least one of these variants encodes a preproprotein that is proteolytically processed to generate the mature protease.