©Institute of Biochemistry and Cell Biology, SIBS, CAS Critical Role of Cys168 in Noggin Protein’s Biological Function

Abstract Previous studies have indicated that noggin exerts its neural inducing effect by binding and antagonizing bone morphogenetic protein 4 (BMP4). In order to further clarify the relationship between the structure and the function of noggin, and elucidate the possible mechanism responsible for noggin-BMP4 interaction, we generated three noggin mutants, C168S, C174S and C197S, by using a site-directed mu-tagenesis method. Ectopic expression of wild-type (WT) noggin, C174S or C197S, in Xenopus animal caps (ACs) by mRNA injection converted the explants (prospective ectoderm) into neural tissue, as indicated by the neural-like morphology and expression of the neural cell adhesion molecule (NCAM) in the ACs. In contrast, ACs expressing C168S suffered an epidermal fate similar to the control caps. Similarly, among the three mutants, only C168S lost the dorsalizing function. These studies highlight the critical role played by Cys168 in noggin’s biological activities. It probably participates in the formation of an intermolecular disulfide bridge. Key words noggin; site-directed mutagenesis; neural induction; dorsalizing The amphibian nervous system is derived from a por-tion of the ectoderm by its interaction with the dorsal mesoderm, which is called Spemann organizer. When trans-planted from one blastula stage embryo to the ventral sid