Incorporation of light-sensitive nonstandard amino acids in pH low insertion peptide for conformation control by light

The development of functional materials has emerged as an intensive area of research in recent years¹. Particularly valuable materials are those designed with properties of ‘‘smart chemical systems”, whose functionality is sensitive to external stimulation². Light is the most attractive stimuli, since photons do not cause sample contamination and have low or negligible toxicity at appropriate wavelengths. Incorporation of nonstandard amino acids (nsAAs) with photosensitive moieties site-specifically can be a valuable tool in the development of light-responsive proteins. Azobenzenes are ubiquitously used as photoswitches in biological applications³ since they are characterized by a simple synthesis process, relatively high photostationary states and quantum yields, fast photoisomerization, and low rate of photobleaching. In this work, we aim to design light-responsive cell-penetrating peptides via incorporation of nsAAs with an Azobenzene moiety. Our protein modal, pH Low Insertion Peptide (pHLIP), is a water-soluble polypeptide derived from the C helix of bacteriorhodopsin which interacts with the membrane at acidic pH (~5.5) to form stable transmembrane α-helix⁴. Our hypothesis is that the Azobenzene isomerization can be used to convert pH to light dependence in this protein. To this end, we examined nsAA substitution at different positions in pHLIP and determined the ability of these modifications to regulate the peptide α-helical structure, with an eye to alter the peptide transmembrane penetration ability.

References:

1. Zhang et al. (2016), Coordination Chemistry Reviews, 319, 180–195.
2. Manrique-Juárez et al. (2016). Coordination Chemistry Reviews, 308, 395-408.
3. Beharry et al. (2011), Chemical Society Reviews, 40(8), 4422-4437.
4. Deacon et al. (2015), Archives of biochemistry and biophysics, 565, 40-48.