Studies of the N-end Rule Pathway in Bacteria and Mammals

Citation

Vu, Tran Minh Tri (2017) Studies of the N-end Rule Pathway in Bacteria and Mammals. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9668B5J. https://resolver.caltech.edu/CaltechTHESIS:07022016-190718870

Abstract

Many intracellular proteins are either conditionally or constitutively short-lived, with in vivo half-lives that can be as brief as a minute or so. The regulated and processive degradation of intracellular proteins is carried out largely by the ubiquitin (Ub)-proteasome system (UPS), in conjunction with molecular chaperones, autophagy, and lysosomal proteolysis. The N-end rule pathway, the first specific pathway of UPS to be discovered, relates the in vivo half-life of a protein to the identity of its N-terminal residue. Physiological functions of the N-end rule pathway are strikingly broad and continue to be discovered. In bacteria and in eukaryotic organelles mitochondria and chloroplasts all nascent proteins bear the pretranslationally formed N-terminal formyl-methionine (fMet) residue. What is the main biological function of this metabolically costly, transient, and not strictly essential modification of N-terminal Met, and why has Met formylation not been eliminated during bacterial evolution? One possibility is that the formyl groups of N-terminal Met in Nt formylated bacterial proteins may signify a proteolytic role of Nt-formylation. My colleagues and I addressed this hypothesis experimentally, as described in Chapter 3 of this thesis.

Among the multitude of biological functions of the mammalian Arg/N-end rule pathway are its roles in the brain, including the regulation of synaptic transmission and the regulation of brain’s G-protein circuits. This regulation is mediated, in part, by the its Ate1-mediated arginylation branch of the Arg/N-end rule pathway. One role of the Ate1 arginyltransferase (R-transferase) is to mediate the conditional degradation of three G-protein down-regulators, Rgs4, Rgs5, and Rgs16. Ate1^-/- mice, which lack the Ate1 R-transferase, exhibit a variety of abnormal phenotypes. Chapter 4 describes our studies of neurological abnormalities in Ate1^-/- mice (and also in mice that express Ate1 conditionally, upon the addition of doxycycline), with an emphasis on the propensity of these mice to epileptic seizures.

Thesis Files