Fig. 1.

Allosteric proteins are sensitive to crowding effects. (a) The mini intein activity can be allosterically modulated by a loop distant from the active site. Two residues in the active site (H73 and N440) are represented by large balls and residues in the loop are represented by small balls and sticks. Three loops with different sizes were tested in [35]. Active intein has a longer loop (VR96DVE99TGE102L404). While reducing the loop length to VR96DVE99…L404 still preserved the activity, further shortening to VR96L404 inactivates the enzyme. (b) The structure of allosteric protein SARS-Co 3CL peptidase, for which the catalytic activity increases in a crowded environment. Three active site residues (H41, S144, and C145) are shown as large balls in one domain. The mutant position N214 is shown as large balls in another domain