Curious about Brazzein
Brazzein is not even a sugar - its a protein that comes from Oubli, a West African climbing plant.  

While I think nearly every living thing from bacteria up to large animals can perceive some carbohydrates as a food source, the mechanisms vary over the tree of life.  

Because of this the taste of sweetness in animals varies a lot.  Aspartame, a non carbohydrate sweetener does not register as sweet in all the primates.  Brazzein and aspartame as capable of activating one or more of the human taste receptors.  Receptors are just proteins which sense a stimulus.  They can be activated by other compounds - this is how most pharmaceuticals work.  Sweeteners which are not glucose/sucrose can bind more tightly or affect the structure of the receptors, causing them to send a sweetness signal. Often these compounds also register with other sense receptors and so the sweetness is accompanied by other tastes as well.  It sounds like Brazzein is a clean taste, less likely to have such side effects.  

I've not dug fully into this - its clear that some human sweetness receptors are known, but I'm not sure they are all known.