Gangalum Rajendra K, Bhat Suraj P
Jules Stein Eye Institute, Geffen School of Medicine, University of California School of Medicine, Los Angeles, California, USA.
Invest Ophthalmol Vis Sci. 2009 Jul;50(7):3283-90. doi: 10.1167/iovs.08-3052. Epub 2009 Feb 14.
All crystallins have non-crystallin catalytic functions. Because catalytic functions do not require large concentrations of protein, as are seen in the lens, there is a perception of dichotomy in the catalytic/physiological function of crystallins within and outside the lens. The status of alphaB-crystallin, a ubiquitously expressed small heat shock protein (and a crystallin) in the ocular lens, was investigated.
Discontinuous sucrose density gradients were used for fractionation of Golgi membranes and vesicles. Light microscopy and confocal microscopy were used for immunolocalization in cultured cells and the native lens.
alphaB-crystallin is highly organized, as indicated by its polar presence in the apical Golgi in lens epithelium and in the perinuclear Golgi streaks in differentiating lens fiber cells. Assessment of the distribution of alphaB-crystallin in Golgi-enriched and vesicular fractions (characterized by the presence of Golgi membrane protein GM130 and vesicle coat protein gammaCOP) in the developing lens reveal a gradual transition from Golgi to vesicular fraction, concomitant with the appearance of alphaB-crystallin as a "soluble" protein.
These data demonstrate that alphaB-crystallin, known to be a soluble protein, starts life as a Golgi-associated membrane protein in the fetal and early postnatal lens and that the developmentally controlled physical state of the Golgi determines the status of this protein in the lens. These findings also show the similarity in the localization/physiological function of alphaB-crystallin within and outside the ocular lens and suggest that non-crystallin/catalytic function is an innate component of the expression of a crystallin in the lens.
所有晶状体蛋白都具有非晶状体蛋白的催化功能。由于催化功能并不需要像晶状体中那样高浓度的蛋白质，因此人们认为晶状体蛋白在晶状体内外的催化/生理功能存在二分法。本研究调查了αB-晶状体蛋白的状态，它是一种在眼晶状体中普遍表达的小分子热休克蛋白（也是一种晶状体蛋白）。
使用不连续蔗糖密度梯度对高尔基体膜和囊泡进行分级分离。利用光学显微镜和共聚焦显微镜对培养细胞和天然晶状体进行免疫定位。
αB-晶状体蛋白高度有序，这表现为它在晶状体上皮细胞顶端高尔基体以及分化的晶状体纤维细胞核周高尔基体条带中的极性存在。对发育中晶状体富含高尔基体和囊泡部分（以高尔基体膜蛋白GM130和囊泡衣被蛋白γCOP的存在为特征）中αB-晶状体蛋白分布的评估显示，随着αB-晶状体蛋白作为“可溶性”蛋白出现，它从高尔基体部分向囊泡部分逐渐转变。
这些数据表明，已知为可溶性蛋白的αB-晶状体蛋白在胎儿期和出生后早期晶状体中最初是一种与高尔基体相关的膜蛋白，并且高尔基体发育控制的物理状态决定了该蛋白在晶状体中的状态。这些发现还显示了αB-晶状体蛋白在眼晶状体内外定位/生理功能的相似性，并表明非晶状体蛋白/催化功能是晶状体蛋白在晶状体中表达的固有组成部分。
