Molecular mechanism for thermal denaturation of thermophilic rhodopsin† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c9sc00855a

Content Provider	Semantic Scholar
Author	Misra, Ramprasad Hirshfeld, Amiram Sheves, Mordechai
Copyright Year	2019
Abstract	Understanding the factors affecting the stability and function of proteins at the molecular level is of fundamental importance. In spite of their use in bioelectronics and optogenetics, factors influencing thermal stability of microbial rhodopsins, a class of photoreceptor protein ubiquitous in nature are not yet well-understood. Here we report on the molecular mechanism for thermal denaturation of microbial retinal proteins, including, a highly thermostable protein, thermophilic rhodopsin (TR). External stimuli-dependent thermal denaturation of TR, the proton pumping rhodopsin of Thermus thermophilus bacterium, and other microbial rhodopsins are spectroscopically studied to decipher the common factors guiding their thermal stability. The thermal denaturation process of the studied proteins is light-catalyzed and the apo-protein is thermally less stable than the corresponding retinal-covalently bound opsin. In addition, changes in structure of the retinal chromophore affect the thermal stability of TR. Our results indicate that the hydrolysis of the retinal protonated Schiff base (PSB) is the rate-determining step for denaturation of the TR as well as other retinal proteins. Unusually high thermal stability of TR multilayers, in which PSB hydrolysis is restricted due to lack of bulk water, strongly supports this proposal. Our results also show that the protonation state of the PSB counter-ion does not affect the thermal stability of the studied proteins. Thermal photo-bleaching of an artificial TR pigment derived from non-isomerizable trans-locked retinal suggests, rather counterintuitively, that the photoinduced retinal trans-cis isomerization is not a pre-requisite for light catalyzed thermal denaturation of TR. Protein conformation alteration triggered by light-induced retinal excited state formation is likely to facilitate the PSB hydrolysis.
Starting Page	7365
Ending Page	7374
Page Count	10
File Format	PDF HTM / HTML
DOI	10.1039/c9sc00855a
PubMed reference number	31489158
Journal	Medline
Volume Number	10
Alternate Webpage(s)	http://www.rsc.org/suppdata/c9/sc/c9sc00855a/c9sc00855a1.pdf
Alternate Webpage(s)	https://doi.org/10.1039/c9sc00855a
Journal	Chemical science
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article