Diarylethene-Based Photoswitchable Inhibitors of Serine Proteases

Abstract

A bicyclic peptide scaffold was chemically adapted to generate diarylethene-based photoswitchable inhibitors of serine protease Bos taurus trypsin 1 (T1). Starting from a prototype molecule-sunflower trypsin inhibitor-1 (SFTI-1)-we obtained light-controllable inhibitors of T1 with K_i in the low nanomolar range, whose activity could be modulated over 20-fold by irradiation. The inhibitory potency as well as resistance to proteolytic degradation were systematically studied on a series of 17 SFTI-1 analogues. The hydrogen bond network that stabilizes the structure of inhibitors and possibly the enzyme-inhibitor binding dynamics were affected by isomerization of the photoswitch. The feasibility of manipulating enzyme activity in time and space was demonstrated by controlled digestion of gelatin-based hydrogel and an antimicrobial peptide BP100-RW. Finally, our design principles of diarylethene photoswitches are shown to apply also for the development of other serine protease inhibitors.

Keywords: bicyclic peptide; diarylethene photoswitch; hydrogel photoregulation; serine protease inhibitors; trypsin.

Figure 1

General design strategies of photoswitchable enzyme inhibitors. The moieties directly binding to enzymes are schematically shown in blue, the photoswitch is shown in red.

Figure 2

Sequence, nomenclature and structure of SFTI‐1. A) Schematic representation of the SFTI‐1 peptide and its structural/functional parts. B) Molecular structure and hydrogen bonding network (PDB: 1JBL). ^[14a]

Figure 3

DAE‐containing amino acid used to prepare the SFTI‐1 analogues, and nomenclature of the photoisomers.

Figure 4

Relationship between T1 inhibitory activity, proteolytic stability, and the number of slow‐exchanging protons in the photoswitchable SFTI‐1 analogues. The ring‐closed to ring‐open changes are indicated by arrows.

Figure 5

Photocontrolled trypsin digestion of gelatin‐based hydrogel in a Petri dish (right); a magnified part of it is shown in the insert (left): A) the area where S10n (ring‐closed) was not irradiated, the gel was digested and removed by a filter paper; B) the area where the ring‐closed S10n was converted to the ring‐open photoform and inhibited trypsin. The hydrogel was stained by bromophenol blue.