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Chapter 8 Lecture Outline
Transcription, Translation, and Bioinformatics
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Transcription, translation
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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8.5 Secretion: Protein Traffic Control
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Protein Traffic Many bacterial proteins reside in cytoplasm Others targeted to other sites Plasma membrane Periplasm Gram outer membrane Secreted outside of bacterium Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Protein Secretion Movement of proteins out of cytoplasm To the periplasm Usually secreted unfolded Require a second set of proteins for correct folding (chaperones) To the outer membrane Across both membranes to the surrounding environment Special export systems are required Move hydrophilic proteins through hydrophobic membrane barriers Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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Protein Export to the Cell Membrane
Proteins for cell membrane (e.g.cytochromes) are tagged with very hydrophobic N-terminal signal sequences Contain hydrophobic transmembrane spanning regions Signal recognition particle (SRP) binds to nascent N-terminus and halt further translation Nascent protein with SRP and ribosome is delivered to the membrane bound protein FtsY Two outcomes Co-translational insertion into cell membrane Complete synthesis and then delivery to SecYEG translocon for insertion Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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SRP and Cotranslational Transport
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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Protein Secretion Animation: Protein Export Click box to launch animation Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Protein Export to Periplasm Examples are superoxide dismutase, maltose binding protein Sec-dependent general pathway Protein completely translated in the cytoplasm Protein captured unfolded by SecB and delivered to SecA and the membrane-bound SecYEG Protein is pushed by SecA through SecYEG in multiple steps LepB cleaves signal sequence Periplasmic chaperones fold the protein Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Protein Secretion to the Outer Surroundings Examples are toxins Type I-VI secretion systems Type I are ABC (ATP Binding cassette) transporters All have three components ABC protein at the inner membrane Periplasmic protein lashed to the inner membrane Outer membrane channel Proteins secreted through Type I never contact the periplasm Example: Hly (E. coli hemolysin) Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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Bioinformatics: Genome Analysis
Genome provides raw DNA sequence What sequences encode proteins? Open reading frames (ORFs) What sequences control expression? Promoters What proteins perform specific functions? Biochemical analysis of protein function Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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Evolutionary Relationships
Sequence reflects ancestry Homologs Orthologs Genes duplicated via appearance of new species Identical function in different organisms Paralogs Genes duplicated within a species Perform slightly different tasks in cell Can develop new capabilities Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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