Gururaja T L, Levine M J
State University of New York at Buffalo, USA.
Pept Res. 1996 Nov-Dec;9(6):283-9.
Human statherin, at low molecular weight (M 5380 Da. 43 amino acid residues) acidic tyrosine-rich phosphoprotein secreted mainly by salivary glands, has been synthesized successfully for the first time following standard solid-phase Fmoc chemistry. Synthesis of this phosphoprotein was accomplished using preformed phosphoserin building blocks. The phosphorylated protein thus synthesized was analyzed and compared with the native molecule and was found to have identical characteristics in its entirety, is evidenced by various analytical methods including mass spectral analysis. Analysis of both the synthetic and native statherin by circular dichroism spectroscopy showed an increase in helicity upon the addition of an organic cosolvent, trifluoroethanol (50%, vol/vol), indicating the presence of potentially amphipathic helical regions. Circular dichroism studies and hydrophobic moment calculations on this synthetic phosphoprotein revealed that the molecule adopts an amphipathic helical conformation at the N-terminus connected to a long poly-L-proline type II segment, which, in turn, is linked to an extended beta-strand. In correlation with previous studies. It appears that the strong binding affinity of statherin for hydroxyapatite can be attributed primarily to the N-terminal sequence, which prefers to adopted helical conformation and provides both electrostatic and hydrogen bonding interactions, thereby inhibiting its mineralization. Production of this highly homogenous synthetic statherin by chemical means may circumvent the prevailing obstacles encountered in conducting its tertiary structural investigations under various physiological conditions.
人组蛋白（分子量5380道尔顿，含43个氨基酸残基）是一种主要由唾液腺分泌的富含酸性酪氨酸的低分子量磷蛋白，首次按照标准的固相Fmoc化学方法成功合成。该磷蛋白的合成使用了预先形成的磷酸丝氨酸构建模块。对如此合成的磷酸化蛋白进行分析并与天然分子比较，发现其整体具有相同特征，各种分析方法（包括质谱分析）都证明了这一点。通过圆二色光谱对合成组蛋白和天然组蛋白进行分析，结果显示加入有机助溶剂三氟乙醇（50%，体积/体积）后螺旋度增加，表明存在潜在的两亲性螺旋区域。对这种合成磷蛋白的圆二色性研究和疏水矩计算表明，该分子在N端呈现两亲性螺旋构象，与一个长的聚-L-脯氨酸II型片段相连，该片段又与一个延伸的β链相连。与先前的研究相关。看来组蛋白对羟基磷灰石的强结合亲和力主要可归因于N端序列，该序列倾向于采用螺旋构象并提供静电和氢键相互作用，从而抑制其矿化。通过化学方法生产这种高度均一的合成组蛋白可能会规避在各种生理条件下进行其三级结构研究时遇到的主要障碍。
