Gupta R S
Department of Biochemistry, McMaster University, Hamilton, Canada.
Mol Microbiol. 1995 Jan;15(1):1-11. doi: 10.1111/j.1365-2958.1995.tb02216.x.
The members of the 10 kDa and 60 kDa heat-shock chaperonin proteins (Hsp10 and Hsp60 or Cpn10 and Cpn60), which form an operon in bacteria, are present in all eubacteria and eukaryotic cell organelles such as mitochondria and chloroplasts. In archaebacteria and eukaryotic cell cytosol, no close homologues of Hsp10 or Hsp60 have been identified. However, these species (or cell compartments) contain the Tcp-1 family of proteins (distant homologues of Hsp60). Phylogenetic analysis based on global alignments of Hsp60 and Hsp10 sequences presented here provide some evidence regarding the evolution of mitochondria from a member of the alpha-subdivision of Gram-negative bacteria and chloroplasts from cyanobacterial species, respectively. This interference is strengthened by the presence of sequence signatures that are uniquely shared between Hsp60 homologues from alpha-purple bacteria and mitochondria on one hand, and the chloroplasts and cyanobacterial hsp60s on the other. Within the alpha-purple subdivision, species such as Rickettsia and Ehrlichia, which live intracellularly within eukaryotic cells, are indicated to be the closest relatives of mitochondrial homologues. In the Hsp60 evolutionary tree, rooted using the Tcp-1 homologue, the order of branching of the major groups was as follows: Gram-positive bacteria--cyanobacteria and chloroplasts--chlamydiae and spirochaetes--beta- and gamma-Gram-negative purple bacteria--alpha-purple bacteria--mitochondria. A similar branching order was observed independently in the Hsp10 tree. Multiple Hsp60 homologues, when present in a group of species, were found to be clustered together in the trees, indicating that they evolved by independent gene-duplication events. This review also considers in detail the evolutionary relationship between Hsp60 and Tcp-1 families of proteins based on two different models (viz. archaebacterial and chimeric) for the origin of eukaryotic cell nucleus. Some predictions of the chimeric model are also discussed.
10 kDa和60 kDa热休克伴侣蛋白（Hsp10和Hsp60或Cpn10和Cpn60）在细菌中形成一个操纵子，存在于所有真细菌以及线粒体和叶绿体等真核细胞器中。在古细菌和真核细胞胞质溶胶中，尚未鉴定出Hsp10或Hsp60的紧密同源物。然而，这些物种（或细胞区室）含有Tcp-1蛋白家族（Hsp60的远亲同源物）。基于此处呈现的Hsp60和Hsp10序列全局比对的系统发育分析分别提供了一些证据，表明线粒体是从革兰氏阴性菌α亚群的一个成员进化而来，叶绿体是从蓝细菌物种进化而来。一方面，α-紫色细菌和线粒体的Hsp60同源物之间独特共享的序列特征，另一方面，叶绿体和蓝细菌hsp60之间独特共享的序列特征，强化了这种关联。在α-紫色亚群中，诸如立克次氏体和埃里希氏体等在真核细胞内寄生的物种被认为是线粒体同源物的最亲近亲属。在以Tcp-1同源物为根的Hsp60进化树中，主要类群的分支顺序如下：革兰氏阳性菌——蓝细菌和叶绿体——衣原体和螺旋体——β-和γ-革兰氏阴性紫色细菌——α-紫色细菌——线粒体。在Hsp10树中独立观察到了类似的分支顺序。当一组物种中存在多个Hsp60同源物时，发现它们在树中聚集在一起，表明它们是通过独立的基因复制事件进化而来的。本综述还基于真核细胞核起源的两种不同模型（即古细菌模型和嵌合模型）详细探讨了Hsp60和Tcp-1蛋白家族之间的进化关系。还讨论了嵌合模型的一些预测。
