Is CureCoin limited to only protein folding?

No! As the network evolves, additional scientific computing projects can be easily added, in which case the folding reward would become a scientific-computation reward, and would be split fairly between various projects (including CPU-only ones!), and could be done so in either a way to encourage people to balance the projects, or in such a way that people can do whatever project they wish, and receive the same or very similar profits.