UV Transition Moments of Tyrosine

Abstract

To assist polarized-light spectroscopy for protein-structure analysis, the UV spectrum of p-cresol, the chromophore of tyrosine, was studied with respect to transition moment directions and perturbation by solvent environment. From linear dichroism (LD) spectra of p-cresol aligned in stretched matrices of poly(vinyl alcohol) and polyethylene, the lowest π-π* transition (Lb) is found to have pure polarization over its entire absorption (250-300 nm) with a transition moment perpendicular to the symmetry axis (C1-C4), both in polar and nonpolar environments. For the second transition (La), polarized parallel with the symmetry axis, a certain admixture of intensity with orthogonal polarization is noticed, depending on the environment. While the Lb spectrum in cyclohexane shows a pronounced vibrational structure, it is blurred in methanol, which can be modeled as due to many microscopic polar environments. With the use of quantum mechanical (QM) calculations, the transition moments and solvent effects were analyzed with the B3LYP and ωB97X-D functionals in cyclohexane, water, and methanol using a combination of implicit and explicit solvent models. The blurred Lb band is explained by solvent hydrogen bonds, where both accepting and donating a hydrogen causes energy shifts. The inhomogeneous solvent-shift sensitivity in combination with robust polarization can be exploited for analyzing tyrosine orientation distributions in protein complexes using LD spectroscopy.

Orientation of aromatic residues in amyloid cores: Structural insights into prion fiber diversity

“…4 C and D) is consistent with one dominating blueshifted fraction of tyrosines oriented near 30°(for L b ) in a nonpolar environment (presumably in the interior of the hydrophobic fiber core). The remaining tyrosines may be blue-shifted or red-shifted, depending on whether they are hydrogen bond donors or hydrogen bond acceptors (38). We think that tyrosines located in "intermediate" regions of the amyloid core (25) are able to adopt different orientations compared with the residues that are buried in the interior of the rigid regions (Fig.…”

“…Our analysis of the LD/A iso ratio shows that some tyrosines in the prion fiber forms experience environmental variations. According to quantum chemical calculations for p-methylphenol, a chromophore of tyrosine, a symmetric broadening of UV bands is expected in a hydroxyl polar environment: Hydrogen bonding between the phenol OH hydrogen and an external oxygen atom is predicted to give a red shift, whereas hydrogen bonding between phenol oxygen and a hydrogen of an OH group is expected to give a blue shift of similar magnitude (2-4 nm) (38). If all tyrosines had been oriented at the same angle and exposed to similar local environments, then the LD spectrum would have had the same shape as the (smeared) absorption spectrum, and LD/A iso had been constant.…”

Flow Alignment of Extracellular Vesicles: Structure and Orientation of Membrane‐Associated Bio‐macromolecules Studied with Polarized Light

“…This also results in increased sensitivity to spectral shifts arising from changes in the local environment. These features can give additional insight into, for example, protein structure by using the aromatic chromophore of tyrosine or tryptophan or by exploiting spectral contribution of exotic chromophores as the heme group in the case of membrane‐associated cytochrome c …”

Impact of modifying the primary structure of cytoplasmic and membrane proteins of the placenta on the development of its insufficiency

“…Снижение в белках содержания остатков глутаминовой и аспарагиновой кислот сопровождалось уменьшением высокореактивных карбоксильных групп, что ограничивало спектр межмолекулярных связей, необходимых для процессов рецепции, транспорта, клеточной трансформации, фолдинга (сворачивания полипептидной цепи в пространственную структуру). Одновременное уменьшение остатков белковосвязанных ароматических аминокислот, представляющих в полипептидной цепи ионизированные участки, также ограничивало регуляторные возможности белков [11,12].…”