The December 2001 issue of Cook's Illustrated magazine included a universal formula for brining. Actually there were two universal formulas, one for the typical meat cooking temperature and another for high-heat cooking such as broiling or grilling. The Cook's Illustrated authors (and many other brining aficionados) complement the salt in a brine with sugar. Though I do not typically use sugar in brines, many people swear it masks or takes the edge off the salt, adds flavor, and promotes browning. (Brining for Flavor)
GB has posted some fabulous links. I can't remember where I read that bit about the sugar being important in the denaturing process (I'll find it eventually!) but most of what I've been reading suggests exactly what GB posted, that the sugar is not essential. It does help in the crisping of the skin and imparting flavor to whatever you brine. I'm off to look at my pork links. I suspect that was where I found it...
Edit: Just this bit,
Once inside the cells, the salt and, to a lesser extent, the sugar cause the cell proteins to unravel, or denature.
You're only given a little spark of madness. You mustn't lose it. Robin Williams Alix