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Extraction of an actin-like protein from the prokaryote Mycoplasma pneumoniae
Abstract:
An actin-like protein has been identified in cell extracts from the prokaryote Mycoplasma pneumoniae. This protein bears a striking resemblance to actin from vertebrates: (i) the solubility of the protein during isolation is analogous to that of actin bound to myosin (soluble in high ionic strength salt solution and insoluble at low ionic strength), (ii) sodium dodecyl sulfate treatment of the partially purified M. pneumoniae extract produces a protein with an electrophoretic mobility very close to that of vertebrate actin in sodium dodecyl sulfate/polyacrylamide gels, (iii) treatment of preparations with ATP-Mg2+ allows separation of long curvilinear filaments, 5-6 nm wide, that closely resemble eukaryotic filamentous actin, and (iv) the prokaryotic filamentous actin binds vertebrate heavy meromyosin fragments to form hybrid compleexes with the characteristic shape of periodic repeating arrowheads, and no heavy meromyosin is bound in the presence of ATP.
Insights
Researchers discovered an actin-like protein in Mycoplasma pneumoniae, a prokaryote. This protein exhibits properties similar to vertebrate actin, forming filaments and binding to myosin fragments.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Actin is a crucial protein in eukaryotic cells, essential for muscle contraction and cell motility.
- The presence of actin homologs in prokaryotes is rare and poorly understood.
Purpose of the Study:
- To investigate the presence and characteristics of actin-like proteins in the prokaryote Mycoplasma pneumoniae.
- To compare the identified protein with vertebrate actin.
Main Methods:
- Isolation of protein from Mycoplasma pneumoniae cell extracts.
- Analysis of protein solubility under varying ionic strengths.
- Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).
- Filament formation studies using ATP-Mg2+.
- Binding assays with vertebrate heavy meromyosin fragments.
Main Results:
- A protein analogous to vertebrate actin was identified in Mycoplasma pneumoniae.
- The protein displayed similar solubility properties to vertebrate actin.
- SDS-PAGE revealed a protein with electrophoretic mobility close to vertebrate actin.
- ATP-Mg2+ treatment induced the formation of 5-6 nm wide curvilinear filaments.
- These filaments bound heavy meromyosin, forming characteristic arrowhead complexes, indicating functional similarity to eukaryotic actin.
Conclusions:
- Mycoplasma pneumoniae possesses an actin-like protein with significant structural and functional similarities to eukaryotic actin.
- This finding suggests a conserved evolutionary role for actin-like proteins across different domains of life.
- The identified protein represents a prokaryotic homolog of actin, offering insights into the evolution of cytoskeletal proteins.