One of the greatest hurdles of engineered therapeutic mechanisms is integrating an efficient solution into a living organism in all its complexity, with minimal loss of product function. In our approach to resolving homocystinuria, it is to be noted that the approach is not to maximize the production of the required enzymes but to keep it, and other metabolites at optimum levels. Achieving this level of finesse in modulating enzyme activity while minimizing perturbations to other integral systems is a direct application of our RBS design tools. Using an array of RBS sequences characterized by expression levels and the predictor optimizer tool, we are able to easily add additional features like kill–switches, whose core toxin-antitoxin system requires fine control over expression activity.