Energetics of surface confined ferritin during iron loading.
We report on the first quantitative picture on how iron loading inside ferritin molecules occurs when they are self-assembled onto solid surfaces. Recombinant human ferritin H-chain with ferroxidase activity was adsorbed onto microcantilever beams to form a stable close-packed thin film. The obtained nanomechanical system was used to track in real time the energetics of inter-ferritin surface interactions during incubation with Fe(II) for iron loading. We observed that iron loading is accompanied by increasing attractive in-plane inter-ferritin interactions able to perform a maximum surface work of 6.0±1.5mJ/m(2), corresponding to a surface energy variation per ferritin of about 40kbT. Unique to this protein surface transformation, part of the surface work is exerted by the attractive electrostatic forces arising among the new born nanosized iron cores inside the ferritin shells. The remaining work comes from subtle action of steric, bridging and depletion forces. These findings are of fundamental interest and add important information for the rational development of ferritin nanotechnology.
Department of Mechanical and Industrial Engineering, University of Brescia, Via Branze 38 25123 Brescia, Italy; National Interuniversity Consortium of Materials Science and Technology (INSTM), Via G Giusti 9, 50121 Firenze, Italy. Electronic address: stefania.federici@unibs.it.
Stefania
S
Federici
Department of Mechanical and Industrial Engineering, University of Brescia, Via Branze 38 25123 Brescia, Italy.
Francesco
F
Padovani
Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123 Brescia, Italy.
Maura
M
Poli
Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123 Brescia, Italy.
Fernando Carmona
FC
Rodriguez
Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123 Brescia, Italy.
Paolo
P
Arosio
Department of Mechanical and Industrial Engineering, University of Brescia, Via Branze 38 25123 Brescia, Italy; National Interuniversity Consortium of Materials Science and Technology (INSTM), Via G Giusti 9, 50121 Firenze, Italy.
Laura E
LE
Depero
Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123 Brescia, Italy; National Interuniversity Consortium of Materials Science and Technology (INSTM), Via G Giusti 9, 50121 Firenze, Italy.
Paolo
P
Bergese
D001052:Apoferritins / Q000378:metabolism*; D005290:Ferric Compounds / Q000737:chemistry; D006801:Humans; D007501:Iron / Q000378:metabolism*; D018625:Microscopy, Atomic Force; D021122:Protein Subunits / Q000378:metabolism; D012815:Signal Processing, Computer-Assisted
D005290:Ferric Compounds; D021122:Protein Subunits; C000499:ferric oxide; D001052:Apoferritins; D007501:Iron
Ferritin; Iron loading; Microcantilevers; Nanomechanics; Surface