Enzyme engineering reaches the boiling point

The boiled enzyme was toppled as a standard enzymology control when researchers in the 1970s started uncovering enzymes that loved the heat (1). Identification of a variety of intrinsically hyperstable enzymes from hyperthermophilic organisms, with optimal growth temperatures of 100°C and above, has piqued academic curiosity (e.g., how do these proteins withstand such ''extreme'' conditions?) and generated considerable interest for their possible applications in biotechnology (2, 3). The realization that enzymes can function at such high temperatures has spawned thermophily-envy, causing researchers and enzyme users to wonder whether their favorite mesophilic enzymes could be engineered to resist boiling, or at least long-term storage on a warm shelf. Perhaps their enzyme has no good thermophilic counterpart, or they do not relish tackling the sometimes considerable technical challenges of working with thermophiles or the enzymes they produce. Thus the literature is replete with testimonials to the power of mutagenesis for protein stabilization (4). With some notable exceptions (5, 6), the increases in stability have been less than impressive.