Bioluminescent imaging systems boosting near-infrared signals in mammalian cells.

Bioluminescence (BL) is broadly used as an optical readout in bioassays and molecular imaging. In this study, the near-infrared (NIR) BL imaging systems were developed. The system was harnessed by prototype copepod luciferases, artificial luciferase 30 (ALuc30) and its miniaturized version picALuc, and were characterized with 17 kinds of coelenterazine (CTZ) analogues carrying bulky functional groups or cyanine 5 (Cy5). They were analyzed of BL spectral peaks and enzymatic kinetics, and explained with computational modeling. The results showed that (1) the picALuc-based system surprisingly boosts the BL intensities predominantly in the red and NIR region with its specific CTZ analogues; (2) both ALuc30- and picALuc-based systems develop unique through-bond energy transfer (TBET)-driven spectral bands in the NIR region with a Cy5-conjugated CTZ analogue (Cy5-CTZ); and (3) according to the computational modeling, the miniaturized version, picALuc, has a large binding pocket, which can accommodate CTZ analogues containing bulky functional groups and thus allowing NIR BL. This study is an important addition to the BL imaging toolbox with respect to the development of orthogonal NIR reporter systems applicable to physiological samples, together with the understanding of the BL-emitting chemistry of marine luciferases.