A Solution NMR Investigation into the Early Events of Amelogenin Nanosphere Self-Assembly Initiated with Sodium Chloride or Calcium Chloride

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• 作者：Garry W. Buchko ; Barbara J. Tarasevich ; Jacky Bekhazi ; Malcolm L. Snead ; Wendy J. Shaw
• 刊名：Biochemistry
• 出版年：2008
• 出版时间：December 16, 2008
• 年：2008
• 卷：47
• 期：50
• 页码：13215-13222
• 全文大小：278K
• 年卷期：v.47,no.50(December 16, 2008)
• ISSN：1520-4995

文摘

Using solution-state NMR spectroscopy, new insights into the early events governing amelogenin supramolecular self-assembly have been identified using sodium chloride and calcium chloride to trigger the association. Two-dimensional ¹H−¹⁵N HSQC spectra were recorded for ¹⁵N- and ¹³C-labeled murine amelogenin as a function of increasing NaCl and CaCl₂ concentration beginning with solution conditions of 2% acetic acid at pH 3.0, where amelogenin was monomeric. Residue specific changes in molecular dynamics, manifested by the reduction in intensity and disappearance of ¹H−¹⁵N HSQC cross-peaks, were observed with the addition of either salt to the protein. With increasing NaCl concentrations, residues between T21 and R31 near the N-terminus were affected first, suggesting that these residues may initiate amelogenin dimerization, the first step in nanosphere assembly. At higher NaCl concentrations, more residues near the N-terminus (Y12−I51) were affected, and with further additions of NaCl, residues near the C-terminus (L141−T171) began to show a similar change in molecular dynamics. With increasing CaCl₂ concentrations, a similar stepwise change in molecular dynamics involving essentially the same set of amelogenin residues was observed. As the concentration of either salt was increased, a concomitant increase in the estimated overall rotational correlation time (τ_c) was observed, consistent with assembly. Self-assembly into a dimer or trimer was established with dynamic light scattering studies under similar conditions that showed an increase in diameter of the smallest species from 4.1 nm in the absence of salt to 10 nm in the presence of salt. These results suggest a possible stepwise interaction mechanism, starting with the N-terminus and followed by the C-terminus, leading to amelogenin nanosphere assembly.