Review The transfer of iron between ceruloplasmin and transferrins ☆ Kenneth N. White a , Celia Conesa b , Lourdes Sánchez b , Maryam Amini c , Sebastien Farnaud d , Chanakan Lorvoralak a , Robert W. Evans c, ⁎ a Institute for Health Research and Policy, Faculty of Life Sciences, London Metropolitan University, London, N7 8DB, UK b Tecnología y Bioquímica de los Alimentos, Facultad de Veterinaria, Universidad de Zaragoza, Miguel Servet 177, 50013, Zaragoza, Spain c Metalloprotein Research Group, Division of Biosciences, School of Health Sciences and Social Care, Brunel University, Uxbridge, Middlesex, UB8 3PH, UK d School of Biosciences, University of Westminster, London W1W 6UW, UK abstract article info Article history: Received 8 June 2011 Received in revised form 10 October 2011 Accepted 15 October 2011 Available online 25 October 2011 Keywords: Ceruloplasmin Ferroxidase Transferrin Lactoferrin Background: It is over 60 years since the discovery and isolation of the serum ferroxidase ceruloplasmin. In that time much basic information about the protein has been elucidated including its catalytic and kinetic properties as an enzyme, expression, sequence and structure. The importance of its biological role is indicated in genetic dis- eases such as aceruloplasminemia where its function is lost through mutation. Despite this wealth of data, funda- mental questions about its action remain unanswered and in this article we address the question of how ferric iron produced by the ferroxidase activity of ceruloplasmin could be taken up by transferrins or lactoferrins. Methods: Overlapping peptide libraries for human ceruloplasmin have been probed with a number of different lactoferrins to identify putative lactoferrin-binding regions on human ceruloplasmin. Docking software, 3D-Gar- den, has been used to model the binding of human lactoferrin to human ceruloplasmin. Results: Upon probing the human ceruloplasmin library with human lactoferrin, three predominantly acidic lac- toferrin-binding peptides, located in domains 2, 5 and 6 of human ceruloplasmin, were identified. The docking software identified a complex such that the N-lobe of human apo-lactoferrin interacts with the catalytic ferroxi- dase centre on human ceruloplasmin. General Significance: In vitro binding studies and molecular modelling indicate that lactoferrin can bind to cerulo- plasmin such that a direct transfer of ferric iron between the two proteins is possible. A direct transfer of ferric iron from ceruloplasmin to lactoferrin would prevent both the formation of potentially toxic hydroxyl radicals and the utilization of iron by pathogenic bacteria. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Part of systemic iron homeostasis involves mobilisation of iron from tissue stores for transport to other regions of the body. Iron exported from tissues such as liver, or from macrophages, leaves the tissue or cells as ferrous iron and is converted to ferric iron by the plasma ferroxidase ceruloplasmin, after which the ferric iron is taken up by the iron transport protein transferrin. Upon activation, macrophages release ferrous iron which is then oxidised by cerulo- plasmin and taken up by lactoferrin. In this report we focus on the molecular interactions between the serum ferroxidase ceruloplasmin and transferrin and lactoferrin. We start by briefly reviewing cerulo- plasmin and its interaction with transferrin and lactoferrin and then present some data from in vitro and modelling studies. 1.1. Ceruloplasmin In 1948, as part of an investigation of the transport of copper in blood, Holmberg and Laurell described the first purification of a blue protein from serum that contained most of the serum copper [1]. They named the protein ceruloplasmin and an investigation of the redox chemistry soon revealed a copper–dependent oxidase enzyme activity, with p-phenylene-diamine the best of a number of substrates tried [2]. The now familiar characteristics of ceruloplasmin oxidase activity, namely inhibition by azide, pH optimum between 5.0 and 6.0 and a requirement for oxygen, were also established [2]. Just prior to the description of ceruloplasmin Holmberg and Laurell had described a distinct iron-binding protein in serum that they named transferrin [3], but it was not until 1960 that the first report of iron, in the form of Fe 2+ , affecting ceruloplasmin activity was published [4]. Ferrous iron had a marked stimulatory effect on ceruloplasmin oxidase activity and at the time it was known that serum possessed strong iron-oxidising activity, but it was not linked to ceruloplasmin. It was also speculated that when iron was loaded onto transferrin it was initially made available as ferrous iron and that oxidation for loading onto transferrin was necessary and was carried out by oxidases of Biochimica et Biophysica Acta 1820 (2012) 411–416 Abbreviations: Cp, ceruloplasmin; Lf, lactoferrin; SAXS, small angle X-ray ☆ This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders. ⁎ Corresponding author. Tel.: + 44 7990703141. E-mail addresses: robertevans49@yahoo.co.uk, Robert.Evans@brunel.ac.uk (R.W. Evans). 0304-4165/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.bbagen.2011.10.006 Contents lists available at SciVerse ScienceDirect Biochimica et Biophysica Acta journal homepage: www.elsevier.com/locate/bbagen