Cloning of Giardia lamblia heat shock protein HSP70 homologs: implications regarding origin of eukaryotic cells and of endoplasmic reticulum.
AUTOR(ES)
Gupta, R S
RESUMO
The genes for two different 70-kDa heat shock protein (HSP70) homologs have been cloned and sequenced from the protozoan Giardia lamblia. On the basis of their sequence features, one of these genes corresponds to the cytoplasmic form of HSP70. The second gene, on the basis of its characteristic N-terminal hydrophobic signal sequence and C-terminal endoplasmic reticulum (ER) retention sequence (Lys-Asp-Glu-Leu), is the equivalent of ER-resident GRP78 or the Bip family of proteins. Phylogenetic trees based on HSP70 sequences show that G. lamblia homologs show the deepest divergence among eukaryotic species. The identification of a GRP78 or Bip homolog in G. lamblia strongly suggests the existence of ER in this ancient eukaryote. Detailed phylogenetic analyses of HSP70 sequences by boot-strap neighbor-joining and maximum-parsimony methods show that the cytoplasmic and ER homologs form distinct subfamilies that evolved from a common eukaryotic ancestor by gene duplication that occurred very early in the evolution of eukaryotic cells. It is postulated that because of the essential "molecular chaperone" function of these proteins in translocation of other proteins across membranes, duplication of their genes accompanied the evolution of ER or nucleus in the eukaryotic cell ancestor. The presence in all eukaryotic cytoplasmic HSP70 homologs (including the cognate, heat-induced, and ER forms) of a number of autapomorphic sequence signatures that are not present in any prokaryotic or organellar homologs provides strong evidence regarding the monophyletic nature of eukaryotic lineage. Further, all eukaryotic HSP70 homologs share in common with the Gram-negative group of eubacteria a number of sequence features that are not present in any archaebacterium or Gram-positive bacterium, indicating their evolution from this group of organisms. Some implications of these findings regarding the evolution of eukaryotic cells and ER are discussed.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=43480Documentos Relacionados
- A heat shock protein gene in Giardia lamblia unrelated to HSP70.
- SSI1 encodes a novel Hsp70 of the Saccharomyces cerevisiae endoplasmic reticulum.
- Identification of heat shock protein hsp70 homologues in chloroplasts.
- Cloning of the Heat Shock Protein 70 (HSP70) Gene of Ehrlichia sennetsu and Differential Expression of HSP70 and HSP60 mRNA after Temperature Upshift
- Major heat shock protein hsp70 protects tumor cells from tumor necrosis factor cytotoxicity.