Formation and stability kinetics of calcium phosphate–fetuin-A colloidal particles probed by time-resolved dynamic light scattering

Abstract

Fetuin-A/α₂-HS glycoprotein is a major systemic inhibitor of unwanted calcium phosphate deposition in the soft tissue. Fetuin-A mediates the formation of initially ∼100 nanometre sized colloidal protein–mineral particles, denoted as calciprotein particles. After a lag period, these particles rapidly grow to elongated particles of about twice the initial size. Similar particles can be generated with other acidic macromolecules as well. However, fetuin-A is more potent regarding activity and specificity of inhibition. Given the widely recognized physiological relevance of fetuin-A as an inhibitor of pathological mineralization both in vitro, in cells, in animals and in humans, and its ready availability in large quantities, fetuin-A is a prototypic model protein to investigate protein–calcium phosphate interactions and mineral colloid stabilization, respectively. Several studies have concentrated on the pathophysiological relevance and the structural details of particle formation and mineral ripening. The principles governing calciprotein particle formation and ripening are nevertheless poorly understood. Here we present a systematic and quantitative investigation by time-resolved dynamic light scattering of the three major parameters: fetuin-A concentration, mineral ion concentration and temperature. Changes in temperature had only a weak effect on calciprotein particle size. Increased mineral ion concentrations and especially increased fetuin-A concentration led to smaller particles. An increased temperature, mineral ion concentration and a reduced fetuin-A concentration, respectively, all accelerated the particle ripening process. Our investigation demonstrates that calciprotein particle formation and ripening are two separate and successive processes and that particle ripening follows Arrhenius law. Furthermore it provides concepts to control the particle size and stability.