Probing a redox switch to save lives : development of a bioassay for angiotensinogen to identify women prone to pre-eclampsia.
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Angiotensinogen is a blood protein that plays a critical role in the regulation of blood pressure in the body. This protein exists in two forms, oxidised and reduced, determined by the presence or absence of a disulfide bridge between Cys 18 and Cys 138. The ratio of oxidised to reduced angiotensinogen is 60:40 in the blood of healthy individuals - an equilibrium that is disrupted in women who develop pre-eclampsia, leading to a higher proportion of oxidised angiotensinogen in the blood. Pre-eclampsia, one of the leading causes of premature births, is a severe and potentially fatal pregnancy condition characterised by the sudden onset of symptoms such as high blood pressure and proteinuria typically during the third trimester. This condition is responsible for an estimated 550,000 deaths globally each year, and with no available treatment or cure other than early delivery of the child, there is a desperate need for a reliable and predictive diagnostic test for this condition.
Can we use angiotensinogen as a biomarker for the early diagnosis of pre-eclampsia? Being able to distinguish between reduced and oxidised angiotensinogen and determine the relative amounts of each in blood samples would be of a huge diagnostic value for this condition. This thesis outlines the expression and purification of recombinant human angiotensinogen in Escherichia coli, and the development of an antibody-based SPR assay for angiotensinogen that was subsequently used to probe whether reduced and oxidised angiotensinogen can be distinguished experimentally. The assay developed was sensitive and reproducible, and demonstrated that the reduced and oxidised forms can be distinguished experimentally. The antibody bound the two forms with differential affinity, due to differences in both the association and dissociation rates of the two forms with the monoclonal antibody.
Finally, in an attempt to further elucidate the differences between the two redox states of angiotensinogen, molecular dynamic simulations were carried out on angiotensinogen in the presence or absence of the disulfide bond between Cys 18 and Cys 138. These simulations revealed some quite striking differences in the dynamics between the two forms. Reduced angiotensinogen was found to be more dynamic in regions critical for binding to renin, providing a possible explanation for the reported differential affinity that renin displays for the two forms.1 Thus, reduced and oxidised angiotensinogen show some quite distinct differences and can be distinguished in an SPR-based assay, highlighting their potential for use as a biomarker in a diagnostic bioassay.