Tandem Mass Spectrometric Evidence for the Involvement of a Lysine Basic Side Chain in the Coordination of Zn(II)Ion within a Zinc-bound Lysine Ternary Complex

摘要

We present the tandem mass spectrometry applications carried out to elucidate the coordination structure of Zn(II)bound lysine ternary complexes,(Zn+Lys+Lys-H)~+,which is a good model system to represent a simple(metallo)enzyme-substrate complex(ES).In particular,experimental efforts were focused on revealing the involvement of a lysine side chain ￡-amino group in the coordination of Zn~(2+)divalent ions.MS/MS fragmentation pattern showed that all the oxygen species within a complex fell off in the form of H_2O in contrast to those of other ternary complexes containing amino acids with simple side chains(4-coordinate geometries,Figure la),suggesting that the lysine complexes have different coordination structures from the others.The participation of a lysine basic side chain in the coordination of Zn(II)was experimentally evidenced in MS/MS for Nepsilon-Acetyl-L-Lys Zn(II)complexes with acetyl protection groups as well as in MS/MS for the ternary complexes with one NH_3 loss,(Zn+Lys+Lys-NH_3-H)~+.Detailed structures were predicted using ab initio calculations on(Zn+Lys+Lys-H)~+ isomers with 4-,5-,and 6-coordinate structures.A zwitterionic 4-coordinate complex(Figure 7d)and a 5-coordinate structure with distorted bipyramidal geometry(Figure 7b)are found to be most plausible in terms of energy stability and compatibility with the experimental observations,respectively.