Interaction of the pre-domain of interleukin-1 with the mature domain

The two interleukin 1 precursors (preIL-1alpha and beta) with a molecular mass of 33 kDa are proteolytically processed to the mature carboxyl-terminal 17-kDa proteins. In this study we newly developed a monoclonal antibody against the precursor domain of IL-1beta (ED7), of which the binding to preIL-1beta was hindered by a polyclonal antibody against the mature domain of IL-1beta. Immunoprecipitation of limited proteolysed preIL-1beta by ED7 suggested that the epitope for ED7 may not be localized at the junction between preIL-1beta and mature IL-1beta. We therefore examined the possibility that the pre-domain of IL-1beta might interact with the mature domain by using chemical cross-linking. V8 protease yielded a mature 17.5-kDa protein from untreated preIL-1beta, but not chemically cross-linked preIL-1beta. However, cleavage of the cross-link with 2-mercaptoethanol liberated a mature 17.5-kDa protein from preIL-1beta, suggesting that the pre-domains of IL-1beta might interact with the mature domain. Similar phenomena were observed with preIL-1alpha. Such an intermolecular interaction may inhibit or modulate the biological activity of mature IL-1s.