Microbial rhodopsins
(MRs) are a diverse and abundant
family of
photoactive membrane proteins that serve as model systems for biophysical
techniques. Optogenetics utilizes genetic engineering to insert specialized
proteins into specific neurons or brain regions, allowing for manipulation
of their activity through light and enabling the mapping and control
of specific brain areas in living organisms. The obstacle of optogenetics
lies in the fact that light has a limited ability to penetrate biological
tissues, particularly blue light in the visible spectrum. Despite
this challenge, most optogenetic systems rely on blue light due to
the scarcity of red-shifted opsins. Finding additional red-shifted
rhodopsins would represent a major breakthrough in overcoming the
challenge of limited light penetration in optogenetics. However, determining
the wavelength absorption maxima for rhodopsins based on their protein
sequence is a significant hurdle. Current experimental methods are
time-consuming, while computational methods lack accuracy. The paper
introduces a new computational approach called RhoMax that utilizes
structure-based geometric deep learning to predict the absorption
wavelength of rhodopsins solely based on their sequences. The method
takes advantage of AlphaFold2 for accurate modeling of rhodopsin structures.
Once trained on a balanced train set, RhoMax rapidly and precisely
predicted the maximum absorption wavelength of more than half of the
sequences in our test set with an accuracy of 0.03 eV. By leveraging
computational methods for absorption maxima determination, we can
drastically reduce the time needed for designing new red-shifted microbial
rhodopsins, thereby facilitating advances in the field of optogenetics.