Access Type

Open Access Thesis

Date of Award

January 2013

Degree Type


Degree Name



Biological Sciences

First Advisor

Choong-Min Kang


Part 1:

One-third of the world's population is infected with the latent form of Mycobacterium tuberculosis. M. tuberculosis must be able to control this latent even in response to nitrosative and oxidative stress conferred by the host. It is not well known how M. tuberculosis controls this state.

One possibility for this control is through its eleven eukaryotic-like serine/threonine protein kinases. Our lab has focused research on two eukaryotic-like ser/thr protein kinases, PknA and PknB. It has been found that PknA expression may affect the stability or the assembly of the proteasome complex, which is essential for M. tuberculosis to persist in mice. This work shows that PknA phosphorylates the α subunit and the unprocessed Β subunit of the M. tuberculosis proteasome, and that this direct effect arrests the proteasome assembly at the half- proteasome stage. Furthermore this effect confers resistance in Mycobacterium smegmatis to oxidative stress.

The significance of this research is that it potentially elucidates one way that M. tuberculosis is able to persist in host cells, because it shows an effect of PknA on a protein complex that is necessary for resistance to nitrosative stress, and whose lack confers resistance to oxidative stress.

Part 2:

L-threonine is the second-most deficient amino acid in livestock, and its addition to livestock feed will create healthier animals and a cleaner environment. Corynebacterium glutamicum is a Grade-A food-safe microorganism that is used for the industrial production of amino acids, which makes it ideal for creating an over-producing strain of threonine.

A key enzyme in the pathway for threonine production in C. glutamicum is homoserine kinase (thrB). Homoserine kinase is competitively inhibited at the active site by threonine, which makes it difficult to relieve feedback inhibition through mutation. This work shows that at the entry of the active site of homoserine kinase there is a conserved alanine residue. We propose that mutation of this residue could relieve feedback inhibition.

The significance of this research is that it provides a novel approach for relief of feedback inhibition, since we attempted to genetically separate the catalytic activity and feedback inhibition in the active site of homoserine kinase. This approach may be applied later to other amino acid production in C. glutamicum and other amino acid over-producing organisms.