Experimental Evaluation of the Density of Water in a Cell by Raman Microscopy

We report direct observation of a spatial distribution of water molecules inside of a living cell using Raman images of the O–H stretching band of water. The O–H Raman intensity of the nucleus was higher than that of the cytoplasm, indicating that the water density is higher in the nucleus than that in the cytoplasm. The shape of the O–H stretching band of the nucleus differed from that of the cytoplasm but was similar to that of the balanced salt solution surrounding cells, indicating less crowded environments in the nucleus. The concentration of biomolecules having C–H bonds was also estimated to be lower in the nucleus than that in the cytoplasm. These results indicate that the nucleus is less crowded with biomolecules than the cytoplasm

Embedding a Metal-Binding Motif for Copper Transporter into a Lipid Bilayer by Cu(I) Binding

Peptide–lipid interactions are widely involved with biologically significant phenomena, including the pathogenic mechanisms of protein misfolding diseases and transmembrane protein folding. In this paper, the interaction of the cysteine/tryptophan (Cys/Trp) motif, which is a metal-binding motif of copper transporter (Ctr) proteins, with a lipid bilayer was studied using fluorescence and circular dichroism (CD) spectroscopy. The binding of Cu­(I) to the Cys/Trp motif induced a large red-edge excitation shift in the Trp fluorescence, indicating that the Trp residue is located inside the lipid bilayer following complexation of Cu­(I) with the Cys/Trp motif. The Stern–Volmer quenching of the Trp fluorescence also supported the Cu­(I) binding peptide embedding in the lipid bilayer. The measurement of the CD spectra indicated the increase in β-sheet content of the Cys/Trp motif peptide as a result of Cu­(I) binding. These results lead to the conclusion that complexation with Cu­(I) induces the change in the secondary structure of the Cys/Trp motif, which results in the peptide embedding in the lipid bilayer. Cu­(I)-induced enhancement of the lipid affinity is discussed in terms of the mechanism for copper transport by Ctr