An approach to understand the complexation of supramolecular dye Congo red with immunoglobulin L chain lambda.
Congo red, a dye of high self-assembling tendency, has been found to form complexes with proteins by adhesion of the ribbon-like supramolecular ligand to polypeptide chains of beta-conformation. Complexation is allowed by local or global protein instability, facilitating penetration of the dye to the locus of its binding. At elevated temperatures, L chain lambda of myeloma origin was found to form two distinct complexes with Congo red, easily differentiated in electrophoresis as slow- and fast-migrating fractions, bearing four- and eight-dye-molecule ligands, respectively, in the V domain of each individual chain. The slow-migrating complex is formed after displacement of the N-terminal polypeptide chain fragment (about 20 residues) from its packing locus, thereby exposing the entrance to the binding cavity. In this work the formation and stability of this complex was studied by molecular dynamics (MD) simulations. The effect of three- and five-molecule ligands introduced to the site binding the dye was also analyzed in an attempt to understand the formation of fast-migrating complexes. The wedging of the ligand containing five dye molecules, hence longer than established experimentally as the maximum for the slow-migrating complex, was found to generate significant structural changes. These changes were assumed to represent the crossing of the threshold on the way to forming a fast-migrating complex more capacious for dyes. They led to almost general destabilization of the V domain, making it susceptible to extra dye complexation. Theoretical studies were designed in close reference to experimental findings concerning the number of dye molecules in the ligand inserted to the site binding the dye, the location of the site in the domain, and the conditions of formation of the complexes. The results of the two kinds of studies appeared coherent.
Król
Marcin
M
Department of Bioinformatics and Telemedicine, Collegium Medicum, Jagiellonian University, Kopernika 17 St., 31-501 Kraków, Poland.
Roterman
Irena
I
Piekarska
Barbara
B
Konieczny
Leszek
L
Rybarska
Janina
J
Stopa
Barbara
B
Spólnik
Paweł
P
Szneler
Edward
E
D019295:Computational Biology; D003198:Computer Simulation; D003224:Congo Red / Q000737:chemistry* / Q000378:metabolism; D007146:Immunoglobulin lambda-Chains / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013057:Spectrum Analysis
D007146:Immunoglobulin lambda-Chains; D003224:Congo Red