Many organisms capture or sense sunlight using rhodopsin pigments, which are integral membrane proteins that bind retinal chromophores. Rhodopsins comprise two distinct protein families , type-1 (microbial rhodopsins) and type-2 (animal rhodopsins). The two families share similar topologies and contain seven transmembrane helices that form a pocket in which retinal is linked covalently as a protonated Schiff base to a lysine at the seventh transmembrane helix. Type-1 and type-2 rhodopsins show little or no sequence similarity to each other, as a consequence of extensive divergence from a common ancestor or convergent evolution of similar structures . Here we report a previously unknown and diverse family of rhodopsins-which we term the heliorhodopsins-that we identified using functional metagenomics and that are distantly related to type-1 rhodopsins. Heliorhodopsins are embedded in the membrane with their N termini facing the cell cytoplasm, an orientation that is opposite to that of type-1 or type-2 rhodopsins. Heliorhodopsins show photocycles that are longer than one second, which is suggestive of light-sensory activity. Heliorhodopsin photocycles accompany retinal isomerization and proton transfer, as in type-1 and type-2 rhodopsins, but protons are never released from the protein, even transiently. Heliorhodopsins are abundant and distributed globally; we detected them in Archaea, Bacteria, Eukarya and their viruses. Our findings reveal a previously unknown family of light-sensing rhodopsins that are widespread in the microbial world.

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The interactions between a Cu-based metal−organic framework (MOF), Cu-BTC, and an ionic liquid (IL), 1-ethyl-3methylimidazolium ethyl sulfate, were studied by employing density functional theory (DFT) calculations and vibrational spectroscopy. The Fourier transform infrared (FTIR) and Raman spectra show that the confinement of the IL in the MOF has significant impact on the structure of the MOF as well as on the IL. Raman spectra and DFT calculations reveal a perturbation of the symmetry of the MOF structure due to the interaction of the IL anion with the Cu ions. FTIR and Raman spectra show that the molecular interactions in turn influence the structure of the ion pair. Inside the MOF, two different types of structure of IL ion pairs are formed. One ion-pair structure exhibits enhanced interionic interactions by strengthening the hydrogen bonding between cation and anion, whereas the other structure corresponds to weaker interactions between the IL cation and anion. Moreover, it is shown that the IL imidazolium ring can directly interact with either the MOF or the anion. The difference electron density analysis by DFT calculations indicates that molecular interactions of MOF and IL are accompanied by a transfer and redistribution of electron density.