Use of mCherryOpt Fluorescent Protein in Clostridium difficile

ABSTRACTFluorescent proteins are powerful reporters in biology, but most require O2for chromophore maturation, making them inherently difficult to use in anaerobic bacteria.Clostridium difficile, a strict anaerobe with a genomic GC content of only 29%, is the leading cause of hospital-acquired diarrhea in developed countries, and new methods for studying this pathogen are sorely needed. We recently demonstrated that a cyan fluorescent protein called CFPoptthat has been codon optimized for production in low-GC bacteria can be used to study protein localization inC. difficileprovided the cells are fixed prior to exposure to air. We describe here a codon-optimized variant of mCherry (mCherryOpt) that exhibits faster acquisition of fluorescence and a better signal-to-noise ratio than CFPopt. We utilizedmCherryOptto construct plasmids for studying protein localization (pRAN473) and gene expression (pDSW1728) inC. difficile. Plasmid pRAN473 is anmCherryOptfusion vector with a tetracycline-inducible promoter. To document its biological utility, we demonstrated septal localization of two cell division proteins, MldA and ZapA. Plasmid pDSW1728 is designed for cloning a promoter of interest upstream ofmCherryOpt. As proof of principle, we studied the expression of thepdaVoperon, which is required for lysozyme resistance. In confirmation and extension of previous reports, we found that expression of thepdaVoperon requires the alternative sigma factor σvand that induction by lysozyme is dose dependent and uniform across the population of lysozyme-treated cells.

Download Full-text

Fluorescent proteins for in vivo imaging, where's the biliverdin?

Biochemical Society Transactions ◽

10.1042/bst20200444 ◽

2020 ◽

Vol 48 (6) ◽

pp. 2657-2667

Author(s):

Felipe Montecinos-Franjola ◽

John Y. Lin ◽

Erik A. Rodriguez

Keyword(s):

Hydrogen Peroxide ◽

In Vivo Imaging ◽

Near Infrared ◽

Fluorescent Protein ◽

Fluorescent Proteins ◽

Fluorescent Imaging ◽

Infrared Light ◽

Red Fluorescent Protein ◽

Color Palette

Noninvasive fluorescent imaging requires far-red and near-infrared fluorescent proteins for deeper imaging. Near-infrared light penetrates biological tissue with blood vessels due to low absorbance, scattering, and reflection of light and has a greater signal-to-noise due to less autofluorescence. Far-red and near-infrared fluorescent proteins absorb light >600 nm to expand the color palette for imaging multiple biosensors and noninvasive in vivo imaging. The ideal fluorescent proteins are bright, photobleach minimally, express well in the desired cells, do not oligomerize, and generate or incorporate exogenous fluorophores efficiently. Coral-derived red fluorescent proteins require oxygen for fluorophore formation and release two hydrogen peroxide molecules. New fluorescent proteins based on phytochrome and phycobiliproteins use biliverdin IXα as fluorophores, do not require oxygen for maturation to image anaerobic organisms and tumor core, and do not generate hydrogen peroxide. The small Ultra-Red Fluorescent Protein (smURFP) was evolved from a cyanobacterial phycobiliprotein to covalently attach biliverdin as an exogenous fluorophore. The small Ultra-Red Fluorescent Protein is biophysically as bright as the enhanced green fluorescent protein, is exceptionally photostable, used for biosensor development, and visible in living mice. Novel applications of smURFP include in vitro protein diagnostics with attomolar (10−18 M) sensitivity, encapsulation in viral particles, and fluorescent protein nanoparticles. However, the availability of biliverdin limits the fluorescence of biliverdin-attaching fluorescent proteins; hence, extra biliverdin is needed to enhance brightness. New methods for improved biliverdin bioavailability are necessary to develop improved bright far-red and near-infrared fluorescent proteins for noninvasive imaging in vivo.

Download Full-text