Biomolecules are constrained by both the chemistry of their constituents as well as the time, place and nature of their function. In proteins, the presence of these constraints leads to tradeoffs between other properties of proteins such as foldability, stability, solubility, etc. and biological function. For the past several years, my group has been studying the effect of the strong constraint of being functional on the folding of diverse proteins. We find that the presence of residues that ensure the accuracy of biological function affect folding in ways which are detectable through simulations of simplified models of proteins. As part of their function, several proteins undergo large conformational transitions. In this talk, I will describe recent work on the folding of two such proteins, what this folding tells us about their free energy landscapes and lessons for the design of new proteins which switch conformations.