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Structural and dynamic properties of translocase motor SecA
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Structural and dynamic properties of translocase motor SecA
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ETD_1531
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http://hdl.rutgers.edu/1782.2/rucore10002600001.ETD.000051299
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eng
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theses
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Topic
Chemistry
Subject
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(authority = ETD-LCSH)
Topic
Translocation (Genetics)
Subject
(ID = SBJ-3);
(authority = ETD-LCSH)
Topic
Cellular control mechanisms
Abstract
SecA is a large, 204 kDa, homodimeric, helicase-like protein that is a key component of the bacteria protein secretion machinery. SecA, being a motor protein, couples the translocation of polypeptide segments across or into biological membranes with the expenditure of metabolic energy extracted from ATP hydrolysis. SecA adopts a compact conformation in the cytoplasm but switches to a relaxed one when is engaged to translocation at the membrane. Specific interaction of SecA with SecYEG induces large conformational changes to both partners that result in the stimulation of SecA’s ATPase activity and trigger the opening of the channel.
We use a combination of NMR spectroscopy, Isothermal Titration Calorimetry (ITC) and biochemical techniques to characterize E. coli SecA along the protein secretion pathway. Recent advances in isotope labeling and NMR methodology (methyl-TROSY) enabled the NMR study of SecA.
We found that the nucleotide binding cleft of SecA exists in a metastable state that undergoes a disorder-order transition upon nucleotide binding. Our data show that SecA uses a novel mechanism wherein conserved regions lining the cleft undergo cycles of disorder-order transitions while switching among functional catalytic states. The structural relation of SecA to helicases suggests that these proteins may utilize similar mechanisms to convert the ATP binding/hydrolysis energy to mechanical work.
Our data reveal that C domain undergoes cycles of detachment and rebinding to the motor that are linked with the ATPase activation of SecA. When the contacts with the C domain are loosened, SecA becomes activated and this process is probably facilitated by the membrane. Moreover, allosteric communication between the preprotein binding and the motor domain of SecA is regulated by nucleotide and signal peptide binding. Finally, we found that the extreme C terminus of SecY (C6 loop) contacts both the motor and the C domain of SecA and we identified important residues from the loop C6 that mediate this interaction.
In summary, our studies revealed the intimate relation between flexibility and catalytic efficiency in SecA as well the allosteric communication among the domains.
We use a combination of NMR spectroscopy, Isothermal Titration Calorimetry (ITC) and biochemical techniques to characterize E. coli SecA along the protein secretion pathway. Recent advances in isotope labeling and NMR methodology (methyl-TROSY) enabled the NMR study of SecA.
We found that the nucleotide binding cleft of SecA exists in a metastable state that undergoes a disorder-order transition upon nucleotide binding. Our data show that SecA uses a novel mechanism wherein conserved regions lining the cleft undergo cycles of disorder-order transitions while switching among functional catalytic states. The structural relation of SecA to helicases suggests that these proteins may utilize similar mechanisms to convert the ATP binding/hydrolysis energy to mechanical work.
Our data reveal that C domain undergoes cycles of detachment and rebinding to the motor that are linked with the ATPase activation of SecA. When the contacts with the C domain are loosened, SecA becomes activated and this process is probably facilitated by the membrane. Moreover, allosteric communication between the preprotein binding and the motor domain of SecA is regulated by nucleotide and signal peptide binding. Finally, we found that the extreme C terminus of SecY (C6 loop) contacts both the motor and the C domain of SecA and we identified important residues from the loop C6 that mediate this interaction.
In summary, our studies revealed the intimate relation between flexibility and catalytic efficiency in SecA as well the allosteric communication among the domains.
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xii, 145 p. : ill.
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Ph.D.
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Includes bibliographical references (p. 131-144)
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by Dimitra Keramisanou
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Keramisanou
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Dimitra
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Dimitra Keramisanou
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Charalambos
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Kalodimos
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Kalodimos G. Charalambos
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Frank
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Jordan
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Jordan Frank
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Phillip
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Huskey
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Huskey Phillip
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John
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Hunf F. John
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Rutgers University
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Graduate School - Newark
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2009
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2009-05
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xx
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Rutgers University Electronic Theses and Dissertations
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Graduate School - Newark Electronic Theses and Dissertations
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doi:10.7282/T33778XH
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ETD doctoral
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The author owns the copyright to this work.
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Copyright protected
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Open
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Keramisanou
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Dimitra
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Dimitra Keramisanou
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Rutgers University. Graduate School - Newark
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I hereby grant to the Rutgers University Libraries and to my school the non-exclusive right to archive, reproduce and distribute my thesis or dissertation, in whole or in part, and/or my abstract, in whole or in part, in and from an electronic format, subject to the release date subsequently stipulated in this submittal form and approved by my school. I represent and stipulate that the thesis or dissertation and its abstract are my original work, that they do not infringe or violate any rights of others, and that I make these grants as the sole owner of the rights to my thesis or dissertation and its abstract. I represent that I have obtained written permissions, when necessary, from the owner(s) of each third party copyrighted matter to be included in my thesis or dissertation and will supply copies of such upon request by my school. I acknowledge that RU ETD and my school will not distribute my thesis or dissertation or its abstract if, in their reasonable judgment, they believe all such rights have not been secured. I acknowledge that I retain ownership rights to the copyright of my work. I also retain the right to use all or part of this thesis or dissertation in future works, such as articles or books.
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