8.A.33.1.5
Cellular retinoic acid binding protein 2, CRABP2 or CRABPII, of 138 aas and possibly 2 TMSs, N- and C-terminal.  It is a microbial rhodopsin mimic, a small soluble protein that photoisomerizes all- trans to 13- cis retinal followed by thermal relaxation to the all- trans isomer, mimicking the bacteriorhodopsin photocycle. The key element for selective isomerization is a tuned steric interaction between the chromophore and protein, similar to that seen in the microbial rhodopsins (Ghanbarpour et al. 2019).