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Dynamic interactions during ribosome targeting to the membrane

dc.contributor.advisorWintermeyer, Wolfgang Prof. Dr.
dc.contributor.authorLee, Sejeong
dc.titleDynamic interactions during ribosome targeting to the membranede
dc.contributor.refereeWintermeyer, Wolfgang Prof. Dr.
dc.description.abstractengThe signal recognition particle (SRP) and its receptor are the main components of the co-translational protein targeting pathway by which membrane proteins are targeted to the membrane. The co-translational targeting pathway is conserved in all organisms. For targeting to the membrane, the membrane proteins contain short hydrophobic patches (about 20 amino acids) at the N-terminus, so called a signal-anchor sequence (SAS). In the bacterial SRP pathway, SRP recognizes a ribosome-nascent chain (RNC) complex by binding to an SAS and forms a targeting complex with its receptor, FtsY. FtsY interacts with SRP and associates with the translocon at the membrane. Thus, from the targeting complex, nascent membrane proteins are transferred to the translocon at the membrane. The targeting complex is formed with high affinity. However, mechanistic details of targeting complex formation and RNC transfer to the translocon are not understood. In this work, the dynamic interactions between SRP and FtsY were analyzed by equilibrium titrations and pre-steady-state kinetics, monitoring FRET between labels introduced in the components of the targeting complex.  We present a mechanism of how the formation of the targeting complex is regulated by the nature of the nascent chain presented on RNCs and how diassembly of the targeting complex and RNC transfer to the translocon is influenced by the nascent chain. The rapid kinetic analysis of targeting complex formation reveals that it takes place in two steps, a bimolecular binding step followed by a conformational change. The conformational change is accelerated on RNCs presenting SAS-containing nascent chains which are about to emerge from the ribosome or already exposed outside the ribosome. Equilibrium studies show that the interaction with the translocon influences binding of FtsY to SRP. In the absence of the RNC, the translocon stabilizes the SRP-FtsY complex. In the presence of ribosomes, the effect is not seen. Instead, the translocon interacts with the ribosome and destabilizes the targeting complex, when the SAS-containing nascent chain reaches a critical length. These observations indicate that the formation and the stability of the targeting complex is regulated by the length of the nascent chain and interaction of the nascent chain containing an SAS with the
dc.contributor.coRefereeFicner, Ralf Prof. Dr.
dc.contributor.thirdRefereeRodnina, Marina Prof. Dr.
dc.contributor.thirdRefereeBennati, Marina Prof. Dr.
dc.contributor.thirdRefereeStark, Holger Prof. Dr.
dc.contributor.thirdRefereeKonrad, Manfred Dr.
dc.subject.engSignal recognition particle, co-translational targeting, E.colide
dc.affiliation.instituteGöttinger Graduiertenschule für Neurowissenschaften, Biophysik und molekulare Biowissenschaften (GGNB)de
dc.subject.gokfullBiologie (PPN619462639)de

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