Very very interesting article…I need to re read it to understand it better…but PlEASE look at the graphs as well…
There’s 2 graphs
endo.endojournals.org/cgi/conten … 147/4/1589
11ß-HSDs and most 17ß-HSDs belong to the short-chain dehydrogenase/reductase (SDR) family (10), a large and diverse group of enzymes. However, 17ß-HSD5 belongs to the aldo-keto reductase (AKR) family, another large enzyme family (11) (med.upenn.edu/akr), which includes other enzymes that regulate steroid hormone access to receptors. One of these AKRs is 3-HSD, which reduces 5-dihydrotestosterone (DHT) to 3-androstanediol (Adiol) while concurrently oxidizing reduced nicotinamide adenine dinucleotide (NAD) phosphate (NADPH) to NAD phosphate (NADP+). In prostate, 3-HSD regulates DHT levels. In this issue, Papari-Zareei et al. (12) show that mutation of arginine-276 to glutamic acid changes the preference of rat 3-HSD from reduction of DHT to dehydrogenation of Adiol, which would have profound effects on cellular DHT levels. Their work is another example of a mechanistic discovery with important clinical applications, which in this case concerns genetic disposition for androgen-dependent diseases such as prostate cancer.
Papari-Zareei et al. (12) focused on altering the interaction of NADP(H) with rat 3-HSD as a way of changing its preference for dehydrogenation of Adiol to DHT in cells. For the most part, cosubstrates have been neglected in studies on metabolism of steroids by SDRs and AKRs. Instead, the focus has been on understanding the interaction between steroid and enzyme with the goal of developing steroid analogs that can regulate steroid hormone levels while ignoring the cosubstrate, which is essential for SDRs and AKRs. Papari-Zareei et al. (12) give cosubstrates well-deserved recognition for their importance in catalysis of steroids by dehydrogenases.
In this respect, Papari-Zareei et al. (12) build on an increasing awareness that the high ratios in cells of NADPH/NADP+ and NAD+/NADH regulate the preference for reduction or oxidation of steroids, respectively, by dehydrogenases. In fact, regeneration of NADPH by enzymes such as hexose-6-phosphate dehydrogenase is crucial for maintaining a ratio of NADPH/NADP+ in cells that will promote reduction of cortisone to cortisol by 11ß-HSD1 (13, 14, 15, 16).
To change the preference of 3-HSD to dehydrogenation of Adiol by altering the interaction with NADP(H), several mutants of Arg-276 were constructed. Arg-276 was chosen for mutagenesis because the three-dimensional (3D) structure of rat 3-HSD cocrystallized with T and NADP+ shows that Arg-276 has a stabilizing interaction with the 2’-phosphate on NADP(H) (17) (Fig. 1A). Papari-Zareei et al. (12) mutated Arg-276 to methionine (R276M), glutamic acid (R276E), and glycine (R276G), each of which has different interactions with oxygens on the 2’-phosphate on NADP+ (Fig. 1B). Met-276 fits nicely with NADP+; Gly-276 lacks a side chain that can stabilize the 2’-phosphate, whereasGlu-276 produces a coulombic interaction that repels NADP+ and destabilizes its binding and also stabilizes binding of NAD+ (Fig. 2). This change in binding of NADPH and NAD+ by the R276E mutant is what would be expected from the 3D structure, because replacement of the 2’-phosphate with a hydroxyl group eliminates the destabilizing coulombic interaction with the side chain on Glu-276 and adds a stabilizing interaction between Glu-276 and the ribose 2’-hydroxyl group.