Department of Biochemistry, NRS Medical College and Hospital, Kolkata 700 014, India.
Protein J. 2010 Nov;29(8):551-6. doi: 10.1007/s10930-010-9289-6.
α-Crystallin functions as a molecular chaperone and maintains transparency of eye lens by protecting other lens-proteins. Non-enzymatic glycation of α-crystallin by methylglyoxal, plays a crucial role on its chaperone function and structural stability. Our studies showed that methylglyoxal modification even in lower concentration caused significant decrease in chaperone function of α-crystallin as reflected both in thermal aggregation assay and enzyme refolding assay. Thermal denaturation studies showed drastic reduction of denaturation temperature with increase in the degree of modification. Thermodynamic stability studies by urea denaturation assay reflected a decrease of transition midpoint. Quantitatively we found that ΔG° of native α-crystallin decreased from 21.6 kJ/mol to 10.4 kJ/mol due to 72 h modification by 10 mM methylglyoxal. The surface hydrophobicity of α-crystallin after MG modification, was found to be decreased. Circular dichroism spectroscopy revealed conversion of ß-sheet structure to random coil structure. Significant cross-linking was also observed due to methylglyoxal modification of human α-crystallin.
α-晶体蛋白作为分子伴侣,通过保护其他晶状体蛋白来维持眼睛晶状体的透明性。由甲基乙二醛引起的α-晶体蛋白的非酶糖基化在其伴侣功能和结构稳定性方面起着至关重要的作用。我们的研究表明,即使在较低浓度下,甲基乙二醛的修饰也会导致α-晶体蛋白伴侣功能显著下降,这在热聚集试验和酶重折叠试验中都有反映。热变性研究表明,随着修饰程度的增加,变性温度急剧下降。脲变性试验的热力学稳定性研究反映了转变中点的降低。定量研究发现,由于 10 mM 甲基乙二醛修饰 72 小时,天然α-晶体蛋白的ΔG°从 21.6 kJ/mol 降低到 10.4 kJ/mol。MG 修饰后α-晶体蛋白的表面疏水性降低。圆二色性光谱显示β-折叠结构向无规卷曲结构的转变。由于人α-晶体蛋白的甲基乙二醛修饰,也观察到明显的交联。