Partial site-specific assignment of a uniformly 13C, 15N enriched membrane protein, light-harvesting complex 1 (LH1), by solid state NMR

Partial site-specific assignments are reported for the solid state NMR spectra of light-harvesting complex 1, a 160 kDa integral membrane protein. The assignments were derived from 600 MHz 15N–13CO–13Cα and 15N–13Cα–13CX correlation spectra, using uniformly 13C, 15N enriched hydrated material, in an intact and precipitated form. Sequential assignments were verified using characteristic 15N–13Cα–13Cβ side chain chemical shifts observed in 3D experiments. Tertiary contacts found in 2D DARR spectra of the selectively 13C enriched sample provided further confirmatory evidence for the assignments. The assignments include the region of the Histidine ligands binding the Bacteriochlorophyll chromophore. The chemical shifts of Cα and Cβ resonances indicated the presence of typical α-helical secondary structure, consistent with previous studies.