School of Life Sciences, Tsinghua University, Beijing, 100084, China.
BMC Genomics. 2010 Mar 25;11:198. doi: 10.1186/1471-2164-11-198.
Cyanobacteria are an ancient group of photoautotrophic prokaryotes with wide variations in genome size and ecological habitat. Metacaspases (MCAs) are cysteine proteinases that have sequence homology to caspases and play essential roles in programmed cell death (PCD). MCAs have been identified in several prokaryotes, fungi and plants; however, knowledge about cyanobacterial metacaspases still remains obscure. With the availability of sequenced genomes of 33 cyanobacteria, we perform a comparative analysis of metacaspases and explore their distribution, domain structure and evolution.
A total of 58 putative MCAs were identified, which are abundant in filamentous diazotrophic cyanobacteria and Acaryochloris marina MBIC 11017 and absent in all Prochlorococcus and marine Synechococcus strains, except Synechococcus sp. PCC 7002. The Cys-His dyad of caspase superfamily is conserved, while mutations (Tyr in place of His and Ser/Asn/Gln/Gly instead of Cys) are also detected in some cyanobacteria. MCAs can be classified into two major families (alpha and beta) based on the additional domain structure. Ten types and a total of 276 additional domains were identified, most of which involves in signal transduction. Apoptotic related NACHT domain was also found in two cyanobacterial MCAs. Phylogenetic tree of MCA catalytic P20 domains coincides well with the domain structure and the phylogenies based on 16s rRNA.
The existence and quantity of MCA genes in unicellular and filamentous cyanobacteria are a function of the genome size and ecological habitat. MCAs of family alpha and beta seem to evolve separately and the recruitment of WD40 additional domain occurs later than the divergence of the two families. In this study, a general framework of sequence-structure-function connections for the metacaspases has been revealed, which may provide new targets for function investigation.
蓝藻是一类古老的光合原核生物，基因组大小和生态生境变化广泛。效应物半胱氨酸蛋白酶（MCAs）是具有与胱冬肽酶序列同源性的半胱氨酸蛋白酶，在程序性细胞死亡（PCD）中发挥重要作用。MCAs已在几种原核生物、真菌和植物中被鉴定出来；然而，关于蓝藻效应物半胱氨酸蛋白酶的知识仍然很不清楚。随着 33 种蓝藻测序基因组的出现，我们对效应物半胱氨酸蛋白酶进行了比较分析，并探讨了它们的分布、结构域结构和进化。
共鉴定出 58 个假定的 MCAs，它们在丝状固氮蓝藻和 Acaryochloris marina MBIC 11017 中丰富，而在所有聚球藻和海洋聚球藻属菌株中均不存在，除了聚球藻属 PCC 7002 外。半胱氨酸-组氨酸二联体是半胱氨酸蛋白酶超家族的保守结构，然而在一些蓝藻中也检测到突变（组氨酸被酪氨酸取代，半胱氨酸被丝氨酸/天冬酰胺/谷氨酰胺/甘氨酸取代）。根据附加结构域，MCAs可分为两大主要家族（alpha 和 beta）。共鉴定出 10 种类型和 276 种附加结构域，其中大多数涉及信号转导。在两种蓝藻效应物半胱氨酸蛋白酶中也发现了与凋亡相关的 NACHT 结构域。MCA 催化 P20 结构域的系统发育树与结构域结构以及基于 16s rRNA 的系统发育非常吻合。
单细胞和丝状蓝藻中 MCA 基因的存在和数量是基因组大小和生态生境的功能。alpha 和 beta 家族的 MCAs似乎分别进化，而 WD40 附加结构域的招募发生在两个家族分化之后。在这项研究中，揭示了效应物半胱氨酸蛋白酶的序列-结构-功能联系的一般框架，这可能为功能研究提供新的目标。
