Spectroscopic Validation of Crystallographic Structures of a Protein Active Site by Chiroptical Spectroscopy.

Out-of-plane distortions of a cofactor molecule in a protein active site are functionally important, and in photoreceptors, it has been proposed that they are crucial for spectral tuning and energy storage in photocycle intermediates. However, these subtle structural features are often beyond the grasp of structural biology. This issue is strikingly exemplified by photoactive yellow protein: its 14 independently determined crystal structures exhibit considerable differences in the dihedral angles defining the chromophore geometry, even though most of these are at excellent resolution.

Spectroscopic ruler for measuring active-site distortions based on Raman optical activity of a hydrogen out-of-plane vibration.

Photoactive yellow protein (PYP), from the phototrophic bacterium , is a small water-soluble photoreceptor protein and contains -coumaric acid (CA) as a chromophore. PYP has been an attractive model for studying the physical chemistry of protein active sites. Here, we explore how Raman optical activity (ROA) can be used to extract quantitative information on distortions of the CA chromophore at the active site in PYP.

Raman optical activity of tetra-alanine in the poly(l-proline) II type peptide conformation.

The poly(l-proline) II (PPII) helix is considered to be a major conformation in disordered polypeptides and unfolded proteins in aqueous solution. The PPII conformation can be identified by using Raman optical activity (ROA), which measures the different intensities of right- and left-circularly polarized Raman scattered light from chiral molecules and provides information on stereochemistry associated with vibrational motions. In the present study, we used tetra-alanine (Ala) as a model system, since its central amide bond adopts the PPII conformation.

Highly efficient NIR to NIR upconversion of ZnMoO:Tm,Yb phosphors and their application in biological imaging of deep tumors.

ZnMoO:Tm,Yb,K nano-phosphors with intense NIR to NIR (excitation by 980 nm, emission at ∼800 nm) upconversion were synthesized by a facile hydrothermal method. The nanoparticles were of the order of 200-400 nm. The XRD patterns confirmed a single phase triclinic structure despite doping small amounts of RE and alkali ions.

Experimental Detection of the Intrinsic Difference in Raman Optical Activity of a Photoreceptor Protein under Preresonance and Resonance Conditions.

Raman optical activity (ROA) is an advanced technique capable of detecting structural deformations of light-absorbing molecules embedded in chromophoric proteins. Resonance Raman (RR) spectroscopy is widely used to enhance the band intensities. However, theoretical work has predicted that under resonance conditions the ROA spectrum resembles the shape of the RR spectrum.