One Retinoid Makes Many Crayons

2 January 2013 by Lowell Goldsmith, posted in JID Jottings

Image from, via a Creative Commons License by Pink_Sherbet_Photography.

Light is essential for many biological processes including  vision, photosynthesis, vitamin D synthesis, and it is useful for treating many skin diseases. The role of the chemical absorbing a specific wavelength of light is always emphasized in elementary photobiology. Sakmar’s recent Science article and the accompanying commentary demonstrate that the chemical environment of a light-absorbing molecule can remarkably affect the wavelength that is absorbed. Not a little difference -- but a very large difference -- in peak absorption; the difference between the same chromophore appearing yellow, with an absorption of 420nm and appearing greenish-blue, with a wavelength of 644 nm. The  absorption of the chromophore, all-trans-retinal,  a  vitamin A-related molecule, was modulated  by its interactions with genetically engineered  variants of  the human cellular retinol binding protein II (CRPII). The approach and chemistry are elegant, and the take-home message is that the  protein changed the electrostatic  density along the polyene portion of the retinoid without affecting the configuration of the retinoid itself.

For those investigating   molecules important for  photobiologic processes, e.g., sunburn, this article reinforces the concept  that it may be necessary to investigate associated molecules as  the chromophore of interest. The pure isolated chromophore may not be yielding the information necessary to understand the process.  In this interesting example, the classical scientific approach of isolating and characterizing  the pure molecule may actually divert the investigator from the in vivo biological process being studied. This finding has profound implications for  those studying and strategizing on the synthesis of  new photoactive molecules. Nature may not yield its secrets to those looking for simple answers.



Sakmar, TP (2012) Redder than Red. Science 338:1299-1300

Wang, W et al (2012) Tuning the electronic absorption of protein-embedded all-trans-retinal. Science 338:1340-1343

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