A Solid-State NMR Study of the Dynamics and Interactions of Phenylalanine Rings in a Statherin Fragment Bound to Hydroxyapatite Crystals

Abstract

Extracellular matrix proteins regulate hard tissue growth by acting as adhesion sites for cells, by triggering cell signaling pathways, and by directly regulating the primary and/or secondary crystallization of hydroxyapatite, the mineral component of bone and teeth. Despite the key role that these proteins play in the regulation of hard tissue growth in humans, the exact mechanism used by these proteins to recognize mineral surfaces is poorly understood. Interactions between mineral surfaces and proteins very likely involve specific contacts between the lattice and the protein side chains, so elucidation of the nature of interactions between protein side chains and their corresponding inorganic mineral surfaces will provide insight into the recognition and regulation of hard tissue growth. Isotropic chemical shifts, chemical shift anisotropies (CSAs), NMR line-width information, (13)C rotating frame relaxation measurements, as well as direct detection of correlations between (13)C spins on protein side chains and (31)P spins in the crystal surface with REDOR NMR show that, in the peptide fragment derived from the N-terminal 15 amino acids of salivary statherin (i.e., SN-15), the side chain of the phenylalanine nearest the C-terminus of the peptide (F14) is dynamically constrained and oriented near the surface, whereas the side chain of the phenylalanine located nearest to the peptide's N-terminus (F7) is more mobile and is oriented away from the hydroxyapatite surface. The relative dynamics and proximities of F7 and F14 to the surface together with prior data obtained for the side chain of SN-15's unique lysine (i.e., K6) were used to construct a new picture for the structure of the surface-bound peptide and its orientation to the crystal surface.

NMR studies of biomineralisation

“…Statherin is a very interesting peptide capable of inhibiting hydroxyapatite crystal growth. The structure and dynamics of this molecule adsorbed on hydroxyapatite surfaces has been studied by solid-state NMR spectroscopy [168][169][170][171][172]. The conformation of the peptide was determined by measuring the distance between introduced 13 C labels using a dipolar recoupling technique (dipolar recoupling with a windowless sequence, DRAWS, see, e.g., Ref.…”

“…The conformation of the peptide was determined by measuring the distance between introduced 13 C labels using a dipolar recoupling technique (dipolar recoupling with a windowless sequence, DRAWS, see, e.g., Ref. [173]) in combination with REDOR (rotational echo double resonance, [174,175]) experiments and T 1q measurements [169][170][171][172].…”

Solid state NMR studies of molecular recognition at protein–mineral interfaces

“…Two samples containing 13 C labels on the phenyl ring of phenylalanine 7 (F7) and phenylalanine 14 (F14) were bound to HAP [89]. Isotropic chemical shifts, chemical shift anisotropies (CSAs), NMR line width information, 13 C rotating frame relaxation measurements, as well as direct detection of correlations between 13 C spins on protein side chains and 31 P spins in the crystal surface with 13 C-31 P REDOR NMR show that in the peptide fragment derived from the N-terminal 15 amino acids of salivary statherin (i.e.…”

Multilayered core–shell structure of polyol-stabilized calcium fluoride nanoparticles characterized by NMR

“…NMR has been increasingly applied over the last few years to investigate the core-surface, core-shell and interface/interphase properties of nanoscale compounds [15,16]. Examples include inner surfaces of zeolites [17][18][19][20][21][22][23][24][25], surface conditioned nanoparticles [26][27][28][29][30][31], carbon nanotubes [32][33][34][35], hydrogen absorption/trapping of nanoparticles [36][37][38], nanocrystalline hydroxyapatite [39][40][41][42][43], non-crystalline nanoparticles [44], polymeric nanoparticles [45,46], inorganic-organic nanocomposites [47,48], and doped nanoparticles [49]. Also biomimetic nanostructures are emerging with increased interest [50,51].…”