Unlocked potential of dynamic elements in protein structures: channels and loops.

Enzymes are nature's powerful catalytic proteins to perform reactions with often outstanding activity, selectivity and specificity. Moreover, the access to non-natural functions of biocatalysts can be facilitated by enzyme engineering. While rational approaches are often focused on an enzyme's active site, from random directed evolution we know that further functional hotspots must exist beyond the active site. Addressing flexible structural elements of these biocatalysts like loops and channels in enzyme engineering has the potential to fill this knowledge gap. The structural dynamics of enzyme catalysts are vital to promote their remarkable functions. This influences for example the access, recognition and orientation of substrates. Herein, we review recent examples of loop and channel engineering and classify them according to their use of simulation methodologies, predictions prior to engineering, the engineering methodologies themselves and discoveries found after the engineering. Thereby we highlight current possibilities and make suggestions to further unlock the potential of this yet underexplored strategy.