Evolution of HSP70 gene and its implications regarding relationships between archaebacteria, eubacteria, and...

Area of Science:

• Molecular Evolution
• Genomics
• Biochemistry

Background:

• The 70-kilodalton heat-shock protein (HSP70) is a highly conserved protein found across all known organisms.
• Identifying conserved and unique sequence signatures is crucial for understanding protein evolution and organismal relationships.
• Archaebacterial HSP70 sequences present unique characteristics, differing from both prokaryotic and eukaryotic homologs.

Purpose of the Study:

• To identify sequence signatures specific to prokaryotic and eukaryotic HSP70 homologs.
• To propose a model for the evolution of the HSP70 gene based on novel sequence features.
• To investigate the phylogenetic relationships between archaebacteria, eubacteria, and eukaryotes using HSP70 sequence data.

Main Methods:

• Global alignment of HSP70 sequences from diverse organisms representing all three domains of life.
• Identification and analysis of specific sequence signatures within HSP70 homologs.
• Phylogenetic analyses using bootstrap, maximum parsimony, and maximum likelihood methods.

Main Results:

• Archaebacterial HSP70 sequences contain eubacterial but lack eukaryotic signature sequences.
• Novel features like tandem repeats and homology to MreB protein inform an evolutionary model for HSP70.
• Phylogenetic analyses reveal archaebacteria are not monophyletic and show a close link with gram-positive eubacteria, contradicting traditional trees.

Conclusions:

• The ancestral form of HSP70 lacks a specific N-terminal insert found in most other homologs.
• Archaebacterial and gram-positive eubacterial HSP70s share a close evolutionary linkage.
• A model proposing eukaryotic cell origins through fusion of archaebacteria and gram-negative eubacteria is supported by HSP70 phylogenies.