Janelia Fluor® 646, Maleimide

Janelia Fluor 646, Maleimide (JF646, Maleimide) is a red fluorescent dye that contains a maleimide group. JF646, Maleimide can be used in cellular imaging ^{[1] [2]}. Janelia Fluor fluorescent dyes can be chemically conjugated to the specific HaloTag substrate (a chloroalkane ligand) to form a fluorescent ligand, rather than binding directly to the HaloTag protein itself. Janelia Fluor products are licensed under U.S. Pat. Nos. 9,933,417, 10,018,624 and 10,161,932 and other patents from Howard Hughes Medical Institute (Ex/Em = 646/664 nm).

In Vitro, Janelia Fluor fluorescent dyes do not inherently possess HaloTag-binding activity; however, reactive groups such as Maleimide serve as reaction sites for covalent coupling-via chemical synthesis-to an amino-functionalized HaloTag chloroalkane ligand scaffold, thereby yielding a fluorescent HaloTag ligand. JF646 can serve as a ligand for self-labeling tag (such as HaloTag)^[1]. JF646, Maleimide is modified by JF646. JF646, a red fluorescent dye, is photostable, membrane-permeable, has a high extinction coefficient^[2].

References:
[1]. Grimm JB, et al. A general method to improve fluorophores for live-cell and single-molecule microscopy. Nat Methods. 2015;12(3):244-250. doi:10.1038/nmeth.3256
[2]. Basu S, et al. FRET-enhanced photostability allows improved single-molecule tracking of proteins and protein complexes in live mammalian cells. Nat Commun. 2018;9(1):2520. Published 2018 Jun 28.