Dynamic footprint of sequestration in the molecular fluctuations of osteopontin

Abstract

The sequestration of calcium phosphate by unfolded proteins is fundamental to the stabilization of biofluids supersaturated with respect to hydroxyapatite, such as milk, blood or urine. The unfolded state of osteopontin (OPN) is thought to be a prerequisite for this activity, which leads to the formation of core-shell calcium phosphate nanoclusters. We report on the structures and dynamics of a native OPN peptide from bovine milk, studied by neutron spectroscopy and small-angle X-ray and neutron scattering. The effects of sequestration are quantified on the nanosecond-ångström resolution by elastic incoherent neutron scattering. The molecular fluctuations of the free phosphopeptide are in agreement with a highly flexible protein. An increased resilience to diffusive motions of OPN is corroborated by molecular fluctuations similar to those observed for globular proteins, yet retaining conformational flexibilities. The results bring insight into the modulation of the activity of OPN and phosphopeptides with a role in the control of biomineralization. The quantification of such effects provides an important handle for the future design of new peptides based on the dynamics-activity relationship.

A Novel 3D Osteoblast and Osteocyte Model Revealing Changes in Mineralization and Pro-osteoclastogenic Paracrine Signaling During Estrogen Deficiency

“…Both proteins increase bone cell adhesion in the mineralized collagen matrix during bone formation (McKee and Nanci, 1996;Giachelli and Steitz, 2000;Malaval et al, 2008). BSP is produced by osteoblasts, while OPN is produced by both osteoblasts and osteoclasts (Denhardt and Noda, 1998;Lenton et al, 2015;Icer and Gezmen-Karadag, 2018). Although BSP acts as an initiator of hydroxyapatite crystal formation in the bone matrix, FIGURE 9 | Constructs under both continued estrogen treatment and estrogen withdrawal (EW) under static conditions and mechanical stimulation.…”

Intrinsically disordered proteins and biomineralization

“…For example, unstructured chains of the milk proteins casein [64] and the SIBLING protein osteopontin [34] are known to stabilize ACP. A recent neutron spectroscopy, small-angle X-ray and neutron scattering of osteopontin-calcium phosphate interactions, confirmed that the 1-149 fragment of osteopontin maintained its flexible linear chain structure in solution, stabilizing ACP particles [115]. Additionally, stabilization of calcium-carbonate nanoparticles and creation of nano-porosities within them is due to the IDP mollusk protein, AP7 [37], discussed above, implying this could be a common IDP –mineral regulation mechanism.…”

Dynamical Oligomerisation of Histidine Rich Intrinsically Disordered Proteins Is Regulated through Zinc-Histidine Interactions

“…In many cases these interactions are directly related to the biological function of the protein [9]. For example, a group of intrinsically disordered phosphoproteins including casein and osteopontin interact with calcium phosphate in milk through phosphorylated residues, thereby stabilising the fluid [10,11,12,13]. Another example is statherin, a saliva protein that transports calcium and magnesium to the enamel, a crucial process required to maintain the mineral phase of teeth [14,15].…”