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Heat shock protein 70 family: multiple sequence comparisons, function, and evolution

S Karlin1, L Brocchieri

  • 1Department of Mathematics, Stanford University, Stanford, CA 94305-2125, USA.

Journal of Molecular Evolution
|November 3, 1998
PubMed
Summary
This summary is machine-generated.

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Heat shock protein 70 kDa (HSP70) sequences are vital molecular chaperones conserved across life. This study analyzes HSP70 conservation, revealing evolutionary insights and functional implications of charge clusters in protein folding and transport.

Area of Science:

  • Molecular Biology
  • Evolutionary Biology
  • Biochemistry

Background:

  • Heat shock protein 70 kDa (HSP70) sequences are crucial molecular chaperones involved in protein folding and transport.
  • HSP70 proteins are highly conserved across all domains of life, including Archaea, eubacteria, and eukaryotes, and are abundant under cellular stress.
  • Understanding HSP70 sequence conservation provides insights into evolutionary relationships and functional mechanisms.

Purpose of the Study:

  • To perform a multiple sequence alignment of a large collection of HSP70 sequences using the ITERALIGN program.
  • To assess conservation patterns in HSP70 sequences in evolutionary and functional contexts.
  • To identify and interpret conserved and divergent sequence features, including signature segments and charge clusters, across different life domains and organelles.

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Main Methods:

  • Multiple sequence alignment of HSP70 sequences using a symmetric-iterative program (ITERALIGN).
  • Comparative analysis of sequence alignments to identify conserved and divergent segments.
  • Development of consensus sequences for eight distinct groups (Archaea, Gram-positive, Gram-negative, singular bacteria, mitochondria, plastids, ER isoforms, cytoplasmic isoforms).
  • Functional interpretation of conserved sequence features, such as charge clusters and conserved residues (tryptophan, cysteine).

Main Results:

  • Many archaeal sequences align best with Gram-positive sequences, and both groups lack a specific 25-amino acid (aa) signature segment found in other HSP70s.
  • A 4-aa signature sequence is present in all prokaryotic HSP70s but absent in eukaryotic homologues.
  • Consensus sequences for different groups improved alignment summarization, with the global consensus matching the consensus of consensuses by 87%.
  • A novel, highly significant mixed charge cluster (EEDKKRRER) was identified near the carboxyl terminus in the global consensus, present in Archaea, Gram-positive, and eukaryotic HSP70s, but notably absent in Gram-negative proteobacterial sequences.
  • Eukaryotic HSP70 isoforms sometimes exhibit multiple mixed charge clusters, suggesting functional roles in chaperone, transport, and secretion.
  • The global consensus contains a single tryptophan and a single conserved cysteine, relevant to protein disaggregation.
  • Mitochondrial HSP70 analysis suggests a polyphyletic split in protist mitochondrial homologues.
  • Entamoeba histolytica HSP70 aligns most closely with higher eukaryotic cytoplasmic sequences, challenging hypotheses about recent mitochondrial loss.

Conclusions:

  • HSP70 sequence analysis reveals significant evolutionary relationships, particularly between archaeal and Gram-positive bacterial sequences.
  • Conserved charge clusters in HSP70 sequences are functionally significant, correlating with chaperone, transport, and secretion activities.
  • The distribution of conserved and divergent sequence features, including signature segments and charge clusters, provides evidence for evolutionary history and functional specialization of HSP70 proteins across diverse organisms.
  • Analysis of HSP70 sequences in organisms like Entamoeba histolytica and Trichomonas vaginalis offers new perspectives on organelle evolution and protein targeting.