This gene encodes a serine protease that plays an important role in the alternative pathway of complement activation for pathogen recognition and elimination. The encoded preproprotein undergoes proteolytic processing to generate a mature, functional enzyme that in turn cleaves factor B in the complement pathway. This gene is expressed in adipocytes and the mature enzyme is secreted into the bloodstream. Mice lacking the encoded product cannot initiate alternative pathway of complement activation. [provided by RefSeq, Jul 2016]