New Far-Red and Near-Infrared Fluorescent Phycobiliproteins with Excellent Brightness and Photostability.

Far-red and near-infrared fluorescent proteins can be used as fluorescence biomarkers in the region of maximal transmission of most tissues and facilitate multiplexing. Recently, we reported the generation and properties of far-red and near-infrared fluorescent phycobiliproteins, termed BeiDou Fluorescent Proteins (BDFPs), which can covalently bind the more readily accessible biliverdin. Far-red BDFPs maximally fluoresce at ∼670 nm, while near-infrared BDFPs fluoresce at ∼710 nm. In this work, we molecularly evolved BDFPs as follows: (a) mutations L58Q, S68R and M81K of BDFPs, which can maximally enhance the effective brightness in vivo by 350 %; (b) minimization and monomerization of far-red BDFPs 2.1, 2.2, 2.3, and near-infrared BDFPs 2.4, 2.5 and 2.6. These newly developed BDFPs are remarkably brighter than the formerly reported far-red and near-infrared fluorescent proteins. Their advantages are demonstrated by biolabeling in mammalian cells using super-resolution microscopy.