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Related Concept Videos

Cotranslational Protein Translocation01:20

Cotranslational Protein Translocation

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Translocation of proteins across membranes is an ancient process that occurs even in bacteria and archaebacteria. In fact, the components of the translocation machinery are still conserved between prokaryotes and eukaryotes.
Sec61 channel partners for cotranslational translocation
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Mitochondrial precursors are translocated to the internal subcompartments via independent mechanisms involving distinct protein machineries called translocases.
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Protein Translocation Machinery on the ER Membrane01:28

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The translocon complex situated on the ER membrane is the main gateway for the protein secretory pathway. It facilitates the transport of nascent peptides into the ER lumen and their insertion into the ER membrane.
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Proteins can form homomeric complexes with another unit of the same protein or heteromeric complexes with different types.  Most protein complexes self-assemble spontaneously via ordered pathways, while some proteins need assembly factors that guide their proper assembly. Despite the crowded intracellular environment, proteins usually interact with their correct partners and form functional complexes.
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Protein Complex Assembly

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Tail-anchoring of Proteins in the ER Membrane01:45

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Tail-anchored, or TA, proteins are estimated to make up to 3-5% of membrane proteins found in the eukaryotic cell. Such proteins have a single transmembrane domain located approximately 30 amino acid residues upstream from the C-terminal end. As a result, the signal recognition particle (SRP) cannot guide a TA protein to the ER membrane for cotranslational insertion. Hence, they are integrated into the ER membrane post-translationally using their C-terminal end as the anchor. TA proteins...
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Evolution of the Translocation and Assembly Module (TAM).

Eva Heinz1, Joel Selkrig2, Matthew J Belousoff1

  • 1Department of Microbiology, Monash University, Melbourne, Victoria, Australia.

Genome Biology and Evolution
|May 22, 2015
PubMed
Summary

The bacterial translocation and assembly module (TAM) likely evolved from BamA and TamB. Gene duplication of BamA led to TamA and TamL, crucial for outer membrane protein assembly in Gram-negative bacteria.

Keywords:
TamATamBbeta-barrel assemblymembrane biogenesisouter membranetranslocation

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Area of Science:

  • Microbiology
  • Protein Folding
  • Evolutionary Biology

Background:

  • Bacterial outer membrane proteins (OMPs) require the beta-barrel assembly machinery (BAM) for proper folding and function.
  • BamA, an Omp85 protein, is the central and essential component of BAM in all Gram-negative bacteria.
  • The translocation and assembly module (TAM), comprising TamA and TamB, is an additional feature of BAM.

Purpose of the Study:

  • To investigate the evolutionary origins and structural characteristics of the TAM components, TamA, TamL, and TamB.
  • To elucidate the phylogenetic distribution and conserved features of the TamB protein family.
  • To propose a model for the evolution of the TAM complex.

Main Methods:

  • Comprehensive phylogenetic analysis of TamB protein family.
  • Secondary structure analysis of TamB.
  • Comparative sequence analysis of TamA, TamL, and TamB.

Main Results:

  • TamA and TamL are predominantly found in Proteobacteria and Bacteroidetes/Chlorobi, respectively.
  • TamB is widely distributed across Gram-negative bacteria and was present early in bacterial evolution.
  • TamB possesses a signal-anchor linkage, beta-helical structure, conserved domains, and a beta-strand-mimicking C-terminus.

Conclusions:

  • The TAM complex likely originated from an ancestral combination of BamA and TamB.
  • A subsequent gene duplication of BamA led to the evolution of TamA and TamL in distinct bacterial lineages.
  • These findings provide insights into the co-evolution of essential protein assembly machinery in Gram-negative bacteria.