Torrado Alejandro, Valladares Ana, Puerto-Galán Leonor, Hervás Manuel, Navarro José A, Molina-Heredia Fernando P
School of Medicine, Department of Anatomy and Neurobiology, Medical Science Campus of the University of Puerto Rico (MCS-UPR), San Juan, PR, USA.
Department of Environmental, Earth and Geospatial Sciences, North Carolina Central University, Durham, North Carolina, USA.
Plant Cell Physiol. 2017 Feb 1;58(2):256-265. doi: 10.1093/pcp/pcw184.
All known cyanobacteria contain Cyt c6, a small soluble electron carrier protein whose main function is to transfer electrons from the Cyt b6f complex to PSI, although it is also involved in respiration. We have previously described a second isoform of this protein, the Cyt c6-like, whose function remains unknown. Here we describe a third isoform of Cyt c6 (here called Cytc6-3), which is only found in heterocyst-forming filamentous cyanobacteria. Cyt c6-3 is expressed in vegetative cells but is specifically repressed in heterocysts cells under diazotrophic growth conditions. Although there is a close structural similarity between Cyt c6-3 and Cyt c6 related to the general protein folding, Cyt c6-3 presents differential electrostatic surface features as compared with Cyt c6, its expression is not copper dependent and has a low reactivity towards PSI. According to the different expression pattern, functional reactivity and structural properties, Cyt c6-3 has to play an as yet to be defined regulatory role related to heterocyst differentiation.
所有已知的蓝藻都含有细胞色素c6（Cyt c6），这是一种小型可溶性电子载体蛋白，其主要功能是将电子从细胞色素b6f复合体转移到光系统I（PSI），不过它也参与呼吸作用。我们之前曾描述过这种蛋白的第二种异构体，即类细胞色素c6，其功能尚不清楚。在此，我们描述细胞色素c6的第三种异构体（此处称为Cytc6-3），它仅在形成异形胞的丝状蓝藻中发现。Cyt c6-3在营养细胞中表达，但在固氮生长条件下的异形胞细胞中受到特异性抑制。尽管Cyt c6-3与细胞色素c6在一般蛋白质折叠方面结构相似，但与细胞色素c6相比，Cyt c6-3呈现出不同的静电表面特征，其表达不依赖于铜，并且对PSI的反应性较低。根据不同的表达模式、功能反应性和结构特性，Cyt c6-3必定在与异形胞分化相关的方面发挥尚未明确的调节作用。
