Structural characterization of the ceruloplasmin: Lactoferrin complex in solution

Ceruloplasmin is a copper protein found in vertebrate plasma, which belongs to the family of multicopper oxidases. Like transferrin of the blood plasma, lactoferrin, the iron-containing protein of human milk, saliva, tears, 2 seminal plasma and of neutrophilic leukocytes tightly binds two ferric ions. Human lactoferrin and ceruloplasmin have been previously shown to interact both in vivo and in vitro forming a complex. Here we describe a study of the conformation of the human lactoferrin/ceruloplasmin complex in solution using small angle X-ray scattering. Our ab initio structural analysis shows that the complex has a 1:1 stoichiometry and suggests that complex formation occurs without major conformational rearrangements of 4 either protein. Rigid-body modeling of the mutual arrangement of proteins in the complex essentially yields two families of solutions. Final discrimination is possible when integrating in the modeling process extra 5 information translating into structural constraints on the interaction between the two partners. (c) 2007 Elsevier Ltd. All rights reserved.