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Originally published In Press as doi:10.1167/iovs.08-3052 on February 14, 2009
 (Investigative Ophthalmology and Visual Science. 2009;50:3283-3290.)
© 2009 by The Association for Research in Vision and Ophthalmology, Inc.
doi:10.1167/iovs.08-3052
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{alpha}B-crystallin: A Golgi-Associated Membrane Protein in the Developing Ocular Lens

Rajendra K. Gangalum1 and Suraj P. Bhat1,2,3

1From the Jules Stein Eye Institute, Geffen School of Medicine, the 2Brain Research Institute, and the 3Molecular Biology Institute, University of California School of Medicine, Los Angeles, California.

PURPOSE. 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 {alpha}B-crystallin, a ubiquitously expressed small heat shock protein (and a crystallin) in the ocular lens, was investigated.

METHODS. 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.

RESULTS. {alpha}B-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 {alpha}B-crystallin in Golgi-enriched and vesicular fractions (characterized by the presence of Golgi membrane protein GM130 and vesicle coat protein {gamma}COP) in the developing lens reveal a gradual transition from Golgi to vesicular fraction, concomitant with the appearance of {alpha}B-crystallin as a "soluble" protein.

CONCLUSIONS. These data demonstrate that {alpha}B-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 {alpha}B-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.






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