S1A16 is a member of S1 protein super family that carries calcium-binding EF-hand motifs. S1 proteins are cell- and tissue-specific and are involved in many intra- and extracellular processes through interacting with specific target proteins. S1A16 expression was found to be astrocyte-specific. The S1A16 protein was found to accumulate within nucleoli and to translocate to the cytoplasm in response to Ca(2+) stimulation. The homodimeric structure of human S1A16 in the apo state has been obtained both in the solid state and in solution, resulting in good agreement between the structures with the exception of two loop regions. The homodimeric solution structure of human S1A16 was also calculated in the calcium(II)-bound form. Differently from most S1 proteins, the conformational rearrangement upon calcium binding is minor. Immunoprecipitation analysis revealed that S1A16 could physically interact with tumor suppressor protein p53, also a known inhibitor of adipogenesis. Overexpression or RNA interference-initiated reduction of S1A16 led to the inhibition or activation of the expression of p53-responsive genes, respectively. S1A16 protein is a novel adipogenesis-promoting factor.