Lens crystallin proteins make up 90% of expressed proteins in the ocular lens and are primarily responsible for maintaining lens transparency and establishing the gradient of refractive index necessary for proper focusing of images onto the retina. Age-related modifications to lens crystallins have been linked to insolubilization and cataractogenesis in human lenses. Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) has been shown to provide spatial maps of such age-related modifications. Previous work demonstrated that, under standard protein IMS conditions, α-crystallin signals dominated the mass spectrum and age-related modifications to α-crystallins could be mapped. In the current study, a new sample preparation method was optimized to allow imaging of β- and γ-crystallins in ocular lens tissue. Acquired images showed that γ-crystallins were localized predominately in the lens nucleus whereas β-crystallins were primarily localized to the lens cortex. Age-related modifications such as truncation, acetylation, and carbamylation were identified and spatially mapped. Protein identifications were determined by top-down proteomics analysis of lens proteins extracted from tissue sections and analyzed by LC-MS/MS with electron transfer dissociation. This new sample preparation method combined with the standard method allows the major lens crystallins to be mapped by MALDI IMS.

中文翻译：

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晶状体中β和γ晶状体蛋白的MALDI成像质谱分析。

晶状体晶状体蛋白占眼晶状体中表达蛋白的90％，主要负责保持晶状体透明性和建立将图像正确聚焦到视网膜上所需的折射率梯度。与年龄相关的晶状体晶状体蛋白修饰已与人晶状体的不溶和白内障发生有关。基质辅助激光解吸/电离（MALDI）成像质谱（IMS）已显示可提供此类年龄相关修饰的空间图。先前的工作表明，在标准蛋白质IMS条件下，α-晶状体蛋白信号占质谱的主导地位，并且可以绘制与年龄相关的对α-晶状体蛋白的修饰的图谱。在当前的研究中，对一种新的样品制备方法进行了优化，以使眼晶状体组织中的β和γ晶状体蛋白成像。所获得的图像显示，γ-晶状蛋白主要位于晶状体核内，而β-晶状蛋白主要位于晶状体皮层。年龄相关的修饰，如截短，乙酰化和氨基甲酰化被鉴定并在空间上作图。通过对从组织切片中提取的晶状体蛋白质进行自上而下的蛋白质组学分析，并通过具有电子转移解离的LC-MS / MS分析，可以确定蛋白质鉴定。这种新的样品制备方法与标准方法相结合，可以通过MALDI IMS对主要晶状体晶体进行定位。通过对从组织切片中提取的晶状体蛋白质进行自上而下的蛋白质组学分析，并通过具有电子转移解离的LC-MS / MS分析，可以确定蛋白质鉴定。这种新的样品制备方法与标准方法相结合，可以通过MALDI IMS对主要晶状体晶体进行定位。通过对从组织切片中提取的晶状体蛋白质进行自上而下的蛋白质组学分析，并通过具有电子转移解离的LC-MS / MS分析，可以确定蛋白质鉴定。这种新的样品制备方法与标准方法相结合，可以通过MALDI IMS对主要晶状体晶体进行定位。