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Membrane assembly: posttranslational insertion of M13 procoat protein into E. coli membranes and its proteolytic

J M Goodman, C Watts, W Wickner

    Cell
    |May 1, 1981
    PubMed

    Insights

    Bacteriophage M13 procoat protein can insert into bacterial membranes after synthesis completion. This post-translational insertion and processing highlights the need for strict criteria in studying cotranslational assembly.

    Area of Science:

    • Molecular biology
    • Virology
    • Membrane protein biogenesis

    Background:

    • Bacteriophage M13 major coat protein is an integral membrane protein.
    • It is synthesized as a precursor (procoat) with a leader sequence.
    • In vivo studies suggest procoat inserts into the plasma membrane post-translationally after synthesis completion.

    Purpose of the Study:

    • To investigate the post-translational insertion of M13 procoat into bacterial membranes.
    • To determine if procoat can be processed into mature coat protein after insertion.
    • To assess the stability and assembly competence of synthesized procoat over time.

    Main Methods:

    • In vitro synthesis of M13 procoat.
    • Incubation with inverted cytoplasmic membrane vesicles from E. coli.
    • Proteolytic processing assays.
    • Analysis of procoat stability and denaturation over time.

    Main Results:

    • M13 procoat demonstrated post-translational insertion into E. coli inverted cytoplasmic membrane vesicles.
    • Proteolytic processing of inserted procoat yielded mature coat protein.
    • Procoat rapidly denatured after synthesis, losing its assembly competence within minutes.
    • Significant denaturation of accumulated procoat occurred during in vitro synthesis.

    Conclusions:

    • M13 procoat can insert into and be processed by bacterial membranes post-translationally.
    • The rapid denaturation of procoat emphasizes the critical timing of protein assembly.
    • These findings underscore the importance of stringent criteria for demonstrating obligate cotranslational assembly.

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