Cross-checking of nanoelectrospray ionization mass spectrometry and computer simulation for the evaluation of the interaction strength of non-covalently bound enkephalins in solution.
Nanoelectrospray ionization mass spectrometry (nanoESI-MS) and computer simulation were applied to the characterization of non-covalent interactions of [Leu5]-enkephalin (LE) and its optical isomers, [D-Tyr1, Leu5]-enkephalin (Y-LE), [D-Phe4, Leu5]-enkephalin (F-LE) and [D-Tyr1, D-Phe4, Leu5]-enkephalin (YF-LE). The dimer formation tendencies of the optical isomers of LE were evaluated by nanoESI-MS using quadruply deuterated LE (H2N-Tyr-(2,2-d2)Gly-(2,2-d2)Gly-Phe-Leu-COOH, d4-LE) as an internal standard. The relative interaction strengths of the optical isomers of LE were estimated to be Y-LE < F-LE < LE < YF-LE. Geometry optimization calculations were performed for interactions in vacuo and in water using a semi-empirical SCF method (PM3). The initial coordinate of the dimer structure of LE was taken from that obtained from single-crystalline x-ray diffraction analysis. Estimates of the interaction strengths of the dimer complexes were based on the heats of formation of a dimer complex (Hd) and the corresponding monomers (Hm) using the equation DeltaH = Hd - 2Hm. The values of DeltaH obtained from the calculations for interactions in water decreased in the order Y-LE > F-LE > LE > YF-LE. Since the smaller values of DeltaH correspond to stronger interactions between peptides, the results from computer simulations were qualitatively consistent with those obtained from the nanoESI experiments. The possibility of cross-checking these independent techniques was demonstrated using medium-sized molecules of biological importance. The agreement of the results from the two techniques suggested that nanoESI experiments, at least qualitatively, reflected the relative interaction strengths of non-covalently bound enkephalins in aqueous solution.
Ishikawa
K
K
National Institute of Materials and Chemical Research, Higashi, Tsukuba, Ibaraki 305-8565, Japan. ishikawa@nimc.go.jp
Nakamura
T
T
Koga
Y
Y
D003198:Computer Simulation; D019281:Dimerization; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives* / Q000737:chemistry*; D004745:Enkephalins / Q000737:chemistry*; D007536:Isomerism; D007700:Kinetics; D008958:Models, Molecular; D011487:Protein Conformation; D012680:Sensitivity and Specificity; D012996:Solutions; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D013329:Structure-Activity Relationship
D004745:Enkephalins; D012996:Solutions; D004743:Enkephalin, Leucine