Selective modification of LMP7 by LKS01 (A) and LKS01-B650 (B) in Panc-1 cells. Panc-1 cells were incubated with LKS01 (0.1, 0.2, 0.5, 1 or 5 μM) or LKS01-B650 (5, 10 or 15 μM) for 1.5 hr and lysed. The resulting cell extracts were electrophoresed and subjected to immunoblotting. LKS01-B650 selectively modified LMP7, but not other proteasome catalytic subunits at the concentrations tested. Epx (epoxomicin, used as positive control). (C) Binding mode of LKS01-B650 with LMP7 active site from X-ray crystal structure.24 An overlay of the LMP7 homology model (gray) used for initial design of LKS01 derivatives with X-ray structure (green) showed a good alignment (right panel). The root-mean-square deviation (RMSD) of the atomic positions of the homology model from the X-ray crystal structure is 1.41 Å which is very small compared to the resolution of the X-ray crystal structure (2.9 Å).