Date of Award


Document Type


Degree Name


Organizational Unit

Physics and Astronomy

First Advisor

Sean E. Shaheen, Ph.D.

Second Advisor

Kingshuk Ghosh

Third Advisor

David Patterson

Fourth Advisor

Dinah Loerke


Adenylosuccinate lyase, Gain in toxic function, Kinetics, Loss of function, Stability


Biophysical tools are becoming more useful in approaching human genetic disease. The pathogenic mechanisms behind many disorders have been attributed to protein loss of function or gain in toxic function. For example, changes in the protein Adenylosuccinate Lyase (ADSL) lead to ADSL deficiency, a disorder that causes symptoms ranging from epilepsy to expression of autistic features. Biophysics offers different tools to study intrinsic properties of proteins. We have applied such tools to study the enzyme kinetics and protein stability of ADSL and two mutations (R426H and R303C) to formulate better hypotheses regarding the pathogenic mechanism. Enzyme kinetic findings indicate a) non-linear dependences of the activities on the substrate ratios due to competitive binding and b) distinct differences in the behaviors of the different mutations. Preliminary stability measurements indicate a) there is an intermediate state in the folding pathway and a fourth state is necessary for modeling, b) R426H, a mutation that causes severe phenotypes, is less stable, c) there is no evidence of a gain in toxic function for either mutation. This complete work supports our hypothesis that there are multiple mechanisms of pathogenesis of ADSL deficiency including instability of the functional ADSL tetramer, aggregation of ADSL, or diminution of enzyme activity. The significance of this is that development of an effective therapy may depend upon which mechanism is active in a particular patient.

Publication Statement

Copyright is held by the author. User is responsible for all copyright compliance.

Rights Holder

Stephen P. Ray


Received from ProQuest

File Format




File Size

276 p.



Included in

Biophysics Commons