Enables aspartic-type peptidase activity; cysteine-type endopeptidase activity; and lipopolysaccharide binding activity. Involved in several processes, including defense response to bacterium; positive regulation of pyroptotic inflammatory response; and self proteolysis. Acts upstream of or within positive regulation of apoptotic process and pyroptotic inflammatory response. Part of NLRP1 inflammasome complex. Is expressed in several structures, including digestive system; heart; immune system; integument; and muscle. Orthologous to human CASP4 (caspase 4).