S100 beta produced in Escherichia coli from a synthetic gene (Van Eldik, L. J., J. L. Staecker, and F. Winningham-Major. 1988. J. Biol. Chem. 263:7830-7837) stimulates neurite outgrowth and enhances cell maintenance in cultures of embryonic chick cerebral cortex neurons. In control experiments, the neurite extension activity is reduced by preincubation with antibodies made against bovine brain S100 beta. When either of the two cysteines in S100 beta are altered by site-directed mutagenesis, the resultant proteins maintain the overall biochemical properties of S100 beta, but lose both the neurite extension and neuronal survival activities. However, another S100 beta mutant, in which the relative position of one of the two cysteines was changed, had neurotrophic activity similar to that of the unmodified protein. These and other results indicate that (a) specific neurite extension activity and neuronal survival activity are two related activities inherent to the S100 beta molecule; (b) a disulfide-linked form of S100 beta is required for full biological activity, and (c) the relative position of the cysteines can be modified. These data suggest potential in vivo roles for S100 beta in the development and maintenance of neuronal function in the central nervous system, and demonstrate the feasibility of the longer term development of selective pharmacological agents based on the S100 beta structure.

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