Plant Cell-Wall Cross-Links by REDOR NMR Spectroscopy

摘要

We present a new method that integrates selective biosynthetic labeling and solid-state NMR detection to identify in situ important protein cross-links in plant cell walls. We have labeled soybean cells by growth in media containing l-[ring-d₄]tyrosine and l-[ring-4-13C]tyrosine, compared whole-cell and cell-wall 13C CPMAS spectra, and examined intact cell walls using 13C{2H} rotational echo double-resonance (REDOR) solid-state NMR. The proximity of 13C and 2H labels shows that 25% of the tyrosines in soybean cell walls are part of isodityrosine cross-links between protein chains. We also used 15N{13C} REDOR of intact cell walls labeled by l-[ε-15N,6-13C]lysine and depleted in natural-abundance 15N to establish that the side chains of lysine are not significantly involved in covalent cross-links to proteins or sugars.