García-Heras Francisco, Padmanabhan S, Murillo Francisco J, Elías-Arnanz Montserrat
Departamento de Genética y Microbiología, Area de Genética (Unidad Asociada al IQFR-CSIC), Facultad de Biología, Universidad de Murcia, Murcia 30100, Spain.
Proc Natl Acad Sci U S A. 2009 Aug 11;106(32):13546-51. doi: 10.1073/pnas.0902233106. Epub 2009 Jul 28.
Histone H1 and high-mobility group A (HMGA) proteins compete dynamically to modulate chromatin structure and regulate DNA transactions in eukaryotes. In prokaryotes, HMGA-like domains are known only in Myxococcus xanthus CarD and its Stigmatella aurantiaca ortholog. These have an N-terminal module absent in HMGA that interacts with CarG (a zinc-associated factor that does not bind DNA) to form a stable complex essential in regulating multicellular development, light-induced carotenogenesis, and other cellular processes. An analogous pair, CarD(Ad) and CarG(Ad), exists in another myxobacterium, Anaeromyxobacter dehalogenans. Intriguingly, the CarD(Ad) C terminus lacks the hallmark HMGA DNA-binding AT-hooks and instead resembles the C-terminal region (CTR) of histone H1. We find that CarD(Ad) alone could not replace CarD in M. xanthus. By contrast, when introduced with CarG(Ad), CarD(Ad) functionally replaced CarD in regulating not just 1 but 3 distinct processes in M. xanthus, despite the lower DNA-binding affinity of CarD(Ad) versus CarD in vitro. The ability of the cognate CarD(Ad)-CarG(Ad) pair to interact, but not the noncognate CarD(Ad)-CarG, rationalizes these data. Thus, in chimeras that conserve CarD-CarG interactions, the H1-like CTR of CarD(Ad) could replace the CarD HMGA AT-hooks with no loss of function in vivo. More tellingly, even chimeras with the CarD AT-hook region substituted by human histone H1 CTR or full-length H1 functioned in M. xanthus. Our domain-swap analyses showing functional equivalence of HMGA AT-hooks and H1 CTR in prokaryotic transcriptional regulation provide molecular insights into possible modes of action underlying their biological roles.
组蛋白H1和高迁移率族A（HMGA）蛋白动态竞争，以调节真核生物中的染色质结构并调控DNA事务。在原核生物中，仅在黄色黏球菌CarD及其橙色小双孢菌直系同源物中发现了类HMGA结构域。这些结构域具有一个在HMGA中不存在的N端模块，该模块与CarG（一种不结合DNA的锌相关因子）相互作用，形成一个稳定的复合物，这对于调节多细胞发育、光诱导类胡萝卜素生成及其他细胞过程至关重要。在另一种黏细菌——脱卤厌氧黏细菌中存在类似的一对蛋白，即CarD(Ad)和CarG(Ad)。有趣的是，CarD(Ad)的C端缺乏标志性的HMGA DNA结合AT钩，反而类似于组蛋白H1的C端区域（CTR）。我们发现，单独的CarD(Ad)无法替代黄色黏球菌中的CarD。相比之下，当与CarG(Ad)一起引入时，尽管CarD(Ad)在体外与CarD相比DNA结合亲和力较低，但CarD(Ad)在调节黄色黏球菌中不仅1个而且3个不同的过程中功能上替代了CarD。同源的CarD(Ad)-CarG(Ad)对相互作用的能力，而非非同源的CarD(Ad)-CarG，使这些数据合理化。因此，在保留CarD-CarG相互作用的嵌合体中，CarD(Ad)的H1样CTR可以替代CarD的HMGA AT钩，而在体内功能无损失。更能说明问题的是，甚至用人类组蛋白H1 CTR或全长H1替代CarD AT钩区域的嵌合体在黄色黏球菌中也能发挥作用。我们的结构域交换分析表明，在原核转录调控中HMGA AT钩和H1 CTR功能等效，这为它们生物学作用背后可能的作用模式提供了分子见解。
