Cameleon is an engineered protein based on variant of

green fluorescent protein The green fluorescent protein (GFP) is a protein that exhibits bright green fluorescence when exposed to light in the blue to ultraviolet range. The label ''GFP'' traditionally refers to the protein first isolated from the jellyfish ''Aequorea ...

used to visualize

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...

levels in living cells. It is a genetically encoded calcium sensor created by

Roger Y. Tsien Roger Yonchien Tsien (pronounced , "'' CHEN''"'';'' February 1, 1952 – August 24, 2016) was an American biochemist. He was a professor of chemistry and biochemistry at the University of California, San Diego and was awarded the Nobel Prize in ...

and coworkers. The name is a conflation of CaM (the common abbreviation of

calmodulin Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the bind ...

) and

chameleon Chameleons or chamaeleons (family Chamaeleonidae) are a distinctive and highly specialized clade of Old World lizards with 202 species described as of June 2015. The members of this family are best known for their distinct range of colors, bein ...

to indicate the fact that the sensor protein undergoes a conformation change and radiates at an altered wavelength upon calcium binding to the calmodulin element of the Cameleon. Cameleon was the first genetically encoded calcium sensor that could be used for ratiometric measurements and the first to be used in a transgenic animal to record activity in neurons and muscle cells. Cameleon and other genetically-encoded calcium indicators (GECIs) have found many applications in

neuroscience Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, development ...

and other fields of biology. It was created by fusing BFP,

, calmodulin-binding peptide M13 and EGFP.{{cite journal , vauthors=Miyawaki A, Llopis J, Heim R , title=Fluorescent indicators for Ca2+ based on green fluorescent proteins and calmodulin , journal=Nature , volume=388 , issue=6645 , pages=882–7 , year=1997 , pmid=9278050 , doi=10.1038/42264, display-authors=etal , bibcode=1997Natur.388..882M, doi-access=free

Mechanism

The DNA encoding cameleon fusion protein must be either stably or transiently introduced into the cell of interest. Protein made by the cell according to this DNA information then serves as a fluorescent indicator of calcium concentration. In the presence of calcium, Ca²⁺ binds to M13, which enables calmodulin to wrap around the M13 domain. This brings the two GFP-variant proteins closer to each other, which increases

FRET A fret is any of the thin strips of material, usually metal wire, inserted laterally at specific positions along the neck or fretboard of a stringed instrument. Frets usually extend across the full width of the neck. On some historical instrume ...

efficiency between them.

References

Sensors Engineered proteins Fluorescent proteins Cell imaging Calcium signaling