Foldamers provide an attractive medium to test the mechanisms by which biological macromolecules fold into complex three-dimensional structures, and ultimately to design novel protein-like architectures with properties unprecedented in nature. Here, we des

© 2015 Nature America, Inc. All rights reserved. Infrared fluorescent proteins (IFPs) provide an additional color to GFP and its homologs in protein labeling. Drawing on structural analysis of the dimer interface, we identified a bacteriophytochrome in the sequence database that is monomeric in truncated form and engineered it into a naturally monomeric IFP (mIFP). We demonstrate that mIFP correctly labels proteins in live cells, Drosophila and zebrafish. It should be useful in molecular, cell and developmental biology.