Wistow G J, Piatigorsky J
Laboratory of Molecular and Developmental Biology, National Eye Institute, National Institutes of Health, Bethesda, MD 20892.
Gene. 1990 Dec 15;96(2):263-70. doi: 10.1016/0378-1119(90)90262-p.
Argininosuccinate lyase(ASL)/delta-crystallin is a prominent example of an enzyme-crystallin with roles as both a catalyst and a major structural component of the eye lens in birds and reptiles. In chicken it appears that gene duplication and separation of function may have occurred with one gene product acting primarily as a crystallin and one primarily as an enzyme. However, two delta-crystallin-encoding genes are abundantly expressed in the lens of the embryonic duck (Anas platyrhynchos) which has extremely high ASL activity. Here the isolation and sequence analysis of full length cDNA clones for both duck delta-crystallins are described. The two delta-crystallins are highly similar (94% identical in predicted aa sequence), probably as a result of gene conversion. However, the cDNA for duck delta 2-crystallin contains an in-frame insertion of two codons, probably the result of a recent intron boundary slippage. ASL/delta-crystallin belongs to a superfamily of lyases, including fumarases, aspartases and adenylosuccinate lyase which possess some highly conserved blocks of aa sequence. There may be some clues to the tertiary structures of these conserved motifs in otherwise unrelated proteins for which three-dimensional structures are known.
精氨琥珀酸裂解酶（ASL）/δ-晶体蛋白是一种典型的兼具酶和晶体蛋白功能的蛋白质，在鸟类和爬行动物的晶状体中，它既是催化剂又是主要的结构成分。在鸡中，似乎发生了基因复制和功能分离，一个基因产物主要作为晶体蛋白起作用，另一个主要作为酶起作用。然而，两个编码δ-晶体蛋白的基因在胚胎鸭（绿头鸭）的晶状体中大量表达，而胚胎鸭具有极高的ASL活性。本文描述了鸭δ-晶体蛋白全长cDNA克隆的分离和序列分析。这两种δ-晶体蛋白高度相似（预测氨基酸序列的同源性为94%），可能是基因转换的结果。然而，鸭δ2-晶体蛋白的cDNA包含两个密码子的读框内插入，这可能是近期内含子边界滑动的结果。ASL/δ-晶体蛋白属于裂合酶超家族，包括延胡索酸酶、天冬氨酸酶和腺苷酸琥珀酸裂解酶，它们拥有一些高度保守的氨基酸序列区域。对于已知三维结构的其他不相关蛋白质，这些保守基序的三级结构可能存在一些线索。
