Ultrafast Vibrational Dynamics of Membrane‐Bound Peptides at the Lipid Bilayer/Water Interface

Vibrational energy transfer (VET) of proteins at cell membrane plays critical roles in controlling the protein functionalities, but its detection is very challenging. By using a surface‐sensitive femtosecond time‐resolved sum‐frequency generation vibrational spectroscopy with infrared pump, the detection of the ultrafast VET in proteins at cell membrane has finally become possible. The vibrational relaxation time of the N−H groups is determined to be 1.70(±0.05) ps for the α‐helix located in the hydrophobic core of the lipid bilayer and 0.9(±0.05) ps for the membrane‐bound β‐sheet structure. The N−H groups with strong hydrogen bonding gain faster relaxation time. By pumping the amide A band and probing amide I band, the vibrational relaxation from N−H mode to C=O mode through two pathways (direct coupling and through intermediate states) is revealed. The ratio of the pathways depends on the NH⋅⋅⋅O=C hydrogen‐bonding strength. Strong hydrogen bonding favors the coupling through intermediate states.     

Breaking the Limits in Analyzing Carbohydrate Recognition by NMR Spectroscopy: Resolving Branch‐Selective Interaction of a Tetra‐Antennary N‐Glycan with Lectins

The biological recognition of complex‐type N ‐glycans is part of many key physiological and pathological events. Despite their importance, the structural characterization of these events remains unsolved. The inherent flexibility of N ‐glycans hampers crystallization and the chemical equivalence of individual branches precludes their NMR characterization. By using a chemoenzymatically synthesized tetra‐antennary N ‐glycan conjugated to a lanthanide binding tag, the NMR signals under paramagnetic conditions discriminated all four N ‐acetyl lactosamine antennae with unprecedented resolution. The NMR data revealed the conformation of the N ‐glycan and permitted for the first time the direct identification of individual branches involved in the recognition by two N ‐acetyllactosamine‐binding lectins, Datura stramonium seed lectin (DSL) and Ricinus Communis agglutinin (RCA120).