Nuclear Magnetic Resonance Secondary Shifts of a Light-Harvesting 2 Complex Reveal Local Backbone Perturbations Induced by Its Higher-Order Interactions

摘要

Protein nuclear magnetic resonance (NMR) secondary chemical shifts are widely used to predictnthe secondary structure, and in solid-state NMR, they are often the only unambiguous structural parametersnavailable. However, the employed prediction methods are empirical in nature, relying on the assumption thatnsecondary shifts are only affected by shielding effects of neighboring atoms.We analyzed the secondary shiftsnof a photosynthetic membrane protein with a high density of chromophores and very tight packing, the light-nharvesting 2 (LH2) complex of Rhodopseudomonas acidophila. A relation was found between secondary shiftnanomalies and protein-protein or pigment-protein tertiary and quaternary contacts. For several residues,nincluding the bacteriochlorophyll-coordinating histidines (RH31 and βH30) and the phenylalanine RF41 thatnhas strongly twisted Cb-Ca-C and Ca-C-N conformations in the LH2 crystal structure, the perturbingneffects on the backbone chemical shifts were tested by density functional theory (DFT) calculations. Wenpropose that higher-order interactions in the tightly packed complex can induce localized perturbations of thenbackbone conformation and electronic structure, related to functional pigment-protein or protein-proteinninteractions.