Sun H, Macke J P, Nathans J
Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Proc Natl Acad Sci U S A. 1997 Aug 5;94(16):8860-5. doi: 10.1073/pnas.94.16.8860.
Diversification of cone pigment spectral sensitivities during evolution is a prerequisite for the development of color vision. Previous studies have identified two naturally occurring mechanisms that produce variation among vertebrate pigments by red-shifting visual pigment absorbance: addition of hydroxyl groups to the putative chromophore binding pocket and binding of chloride to a putative extracellular loop. In this paper we describe the use of two blue-shifting mechanisms during the evolution of rodent long-wave cone pigments. The mouse green pigment belongs to the long-wave subfamily of cone pigments, but its absorption maximum is 508 nm, similar to that of the rhodopsin subfamily of visual pigments, but blue-shifted 44 nm relative to the human red pigment, its closest homologue. We show that acquisition of a hydroxyl group near the retinylidene Schiff base and loss of the chloride binding site mentioned above fully account for the observed blue shift. These data indicate that the chloride binding site is not a universal attribute of long-wave cone pigments as generally supposed, and that, depending upon location, hydroxyl groups can alter the environment of the chromophore to produce either red or blue shifts.
在进化过程中，视锥色素光谱敏感性的多样化是色觉发展的前提条件。先前的研究已经确定了两种自然发生的机制，它们通过使视觉色素吸收峰红移来产生脊椎动物色素之间的差异：在假定的发色团结合口袋中添加羟基以及氯离子与假定的细胞外环结合。在本文中，我们描述了啮齿动物长波视锥色素进化过程中两种蓝移机制的作用。小鼠绿色色素属于视锥色素的长波亚家族，但其最大吸收峰为508nm，与视紫红质视觉色素亚家族相似，但相对于其最接近的同源物——人类红色色素，蓝移了44nm。我们表明，在视黄醛席夫碱附近获得一个羟基以及上述氯离子结合位点的丧失，完全可以解释观察到的蓝移现象。这些数据表明，氯离子结合位点并非如通常所认为的那样是长波视锥色素的普遍特征，并且根据位置不同，羟基可以改变发色团的环境，从而产生红移或蓝移。
