Abstract
Noncovalent interactions between ligands and targeting proteins are essential for understanding molecular mechanisms of proteins. In this work, we investigated the interaction of Cytochrome c (Cyt c) with maltoligosaccharides, namely maltose (Mal II), maltotriose (Mal III), maltotetraose (Mal IV), maltopentaose (Mal V), maltohexaose (Mal VI) and maltoheptaose (Mal VII). Using electrospray ionization mass spetrometry (ESI-MS) assay, the 1:1 and 1:2 complexes formed by Cyt c with maltoligosaccharide ligand were observed. The corresponding association constants were calculated according to the deconvoluted spectra. The order of the relative binding affinities of the selected oligosaccharides with Cyt c were as Mal III > Mal IV > Mal II > Mal V > Mal VI > Mal VII. The results indicated that the stability of noncovalent protein complexes was intimately correlated to the molecular structure of bound ligand. The relevant functional groups that could form H-bonds, electrostatic or hydrophobic forces with protein's amino residues played an important role for the stability of protein complexes. In addition, the steric structure of ligand was also critical for an appropriate interaction with the binding pocket of proteins.