Date of Graduation

12-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry (PhD)

Degree Level

Graduate

Department

Chemistry & Biochemistry

Advisor

Suresh Thallapuranam

Committee Member

Paul Adams

Second Committee Member

Ralph Henry

Third Committee Member

Colin Heyes

Fourth Committee Member

Frank Millett

Fifth Committee Member

Julie Stenken

Abstract

Targeting of proteins is a critical component of cellular function. A universally conserved targeting system of the cytosol utilizes a signal recognition particle (SRP) to target many proteins contranslationally to the endoplasmic reticulum in eukaryotes or the inner membrane in prokaryotes. A homologous SRP system exists in the chloroplast that delivers light harvesting chlorophyll binding proteins (LHCP) to they thylakoid membrane. The chloroplast SRP (cpSRP) is a heterodimer composed of a novel 43 kDa subunit and a 54 kDa subunit homologous to a component of the SRP system, SRP54. Many details regarding the interactions between the proteins of the cpSRP system have been determined. However, the three-dimensional arrangement of the cpSRP43 and cpSRP54 domains as well as their influence on one another has not been determined. The results of this study demonstrate both cpSRP43 and cpSRP54 are characterized by a significant amount of structural flexibility. Specifically, the domains of cpSRP43 and cpSRP54 are flexibly linked allowing for rapid conformational sampling of the domains. This flexibility allows cpSRP43 to sense the presence of cpSRP54 and subsequently alter its affinity for LHCP. Conversely, cpSRP54 domain flexibility allows it to scan cpSRP43 for the third transmembrane segment of LHCP in a manner surprisingly similar to SRP54 scanning for signal sequences at the ribosome. Together, the results of this structural investigation of the free and bound proteins has lead to the speculation of a cpSRP-LHCP transit complex structure capable of rationalizing the steps leading to the integration of LHCP.

Available for download on Sunday, April 19, 2020

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