Alpha A- and alpha B-crystallin in the retina. Association with the post-Golgi compartment of frog retinal photoreceptors.
alpha A- and alpha B-Crystallins are significant contributors to maintaining the transparency of the vertebrate lens. We have found that both alpha A- and alpha B-crystallins are also present, at approximately equimolar concentrations, in frog retinal cells. They were identified by sequencing portions of each polypeptide, by immunochemical cross-reactivity with antibodies to bovine alpha-crystallins, and by their relative mobility in two-dimensional gel electrophoresis. Retinal alpha-crystallins form macromolecular multimeric complexes similar to those found in the lens, and they are abundant both in soluble and membrane-associated forms. A surprising finding is that alpha-crystallins bind specifically to the photoreceptor post-Golgi membranes that mediate transport of newly synthesized rhodopsin. Upon treatment of post-Golgi membranes with urea or Triton X-114, a portion of the bound alpha B-crystallin remains tightly associated, indicating that the alpha B-form may mediate membrane binding of an alpha-crystallin multimeric complex. Both subunits are synthesized in vitro by isolated frog retinas, but alpha B-crystallin appears to have a higher renewal rate. Newly synthesized alpha-crystallins become associated with the post-Golgi membranes concurrently with newly synthesized rhodopsin. Association of alpha-crystallins with newly synthesized rhodopsin suggests that they may participate in photoreceptor outer segment membrane renewal. Our findings implicate an important function for both alpha A- and alpha B-crystallins in the same, extralenticular, tissue.
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Department of Pathology, University of Texas Health Science Center, San Antonio 78284-7750.
Aebersold
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Morrison
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Papermaster
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D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D006224:Cricetinae; D003459:Crystallins / Q000032:analysis* / Q000737:chemistry* / Q000648:ultrastructure; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D006056:Golgi Apparatus / Q000737:chemistry*; D007425:Intracellular Membranes / Q000737:chemistry*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D010786:Photoreceptor Cells / Q000737:chemistry*; D011485:Protein Binding; D011898:Ranidae; D012160:Retina / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000737:chemistry
D003459:Crystallins; D010446:Peptide Fragments