Endocrine Abstracts

Congenital adrenal hyperplasia (CAH) summarizes a group of genetic disorders of enzymes involved in cortisol biosynthesis. The most common causes detrimental mutations in the steroidogenic cytochrome P450 enzyme 21-hydroxylase (CYP21A2). Patients are dependent on a lifelong oral cortisol replacement therapy to ensure survival but quality of life is often reduced and co-morbidities are substantially increased. Also, the administered supraphysiological glucocorticoid dosescannot ideally mimic the circadian rhythm and stress adaption of cortisol secretion. Therefore, the goal of our research is to better understand the specific biophysico-chemical pathomechanism of functional 21-hydroxylase deficiency in order to develop new causative therapeutic approaches. In this work, we investigated the structural and stability properties of six clinically relevant mutant variants of CYP21A2 (V282G/L, P31L, D323G, R484Q/W).Structural and thermal stability were assessed by circular dichroism (CD) spectroscopy. Wild type enzyme showed high α-helical content (65% α-helix) as well as mutants at the position 282 (V282G: 60.6 %, V282L: 57.6%).The α-helical organization in other variants (P31L, D323G, R484Q/W) was more disrupted (42 − 48%) in exchange for mainly random coil. Thermal stability of all mutant variants was reduced (Tm: 41.5 − 45.1°C) compared to the WT (Tm: 47.6°C) in temperature dependent CD spectroscopy. Tryptophan fluorescence experiments to assess denaturant stability of mutant variants also showed higher susceptibility to local unfolding (3.42 − 4.30 M urea) at the hydrophobic core compared to WT using urea as denaturant. Furthermore, in UV/Vis spectroscopy at 280 nm and 418 nm we could demonstrate that all mutant variants had a reduced heme incorporation (A418/A280: 0.20 − 0.63) compared to WT (A418/A280: 0.88). Our results show that correct structural folding and stability pose a major problem in specific mutations involved in CAH. Therefore we propose that structural protein instability plays a key role in the pathophysiology of CAH and thus might constitute a novel tailored therapeutic target for the treatment of affected patients.