Structure and role of the linker domain of the iron surface-determinant protein IsdH in heme transportation in Staphylococcus aureus.

Staphylococcus aureus is a major cause of deadly nosocomial infections, a severe problem fueled by the steady increase of resistant bacteria. The iron surface determinant (Isd) system is a family of proteins that acquire nutritional iron from the host organism, helping the bacterium to proliferate during infection, and therefore represents a promising antibacterial target. In particular, the surface protein IsdH captures hemoglobin (Hb) and acquires the heme moiety containing the iron atom. Structurally, IsdH comprises three distinctive NEAr-iron Transporter (NEAT) domains connected by linker domains. The objective of this study was to characterize the linker region between NEAT2 and NEAT3 from various biophysical viewpoints and thereby advance our understanding of its role in the molecular mechanism of heme extraction. We demonstrate the linker region contributes to the stability of the bound protein, likely influencing the flexibility and orientation of the NEAT3 domain in its interaction with Hb, but only exerts a modest contribution to the affinity of IsdH for heme. Based on these data, we suggest that the flexible nature of the linker facilitates the precise positioning of NEAT3 to acquire heme. In addition, we also found that residues His45 and His89 of Hb located in the heme transfer route toward IsdH do not play a critical role in the transfer rate-determining step. In conclusion, this study clarifies key elements of the mechanism of heme extraction of human Hb by IsdH, providing key insights into the Isd system and other protein systems containing NEAT domains.

Genetics, structure, function, mode of actions and role in cancer development of CYP17.

Most prostate and breast cancers are hormone dependent. The inhibition of steroid 17α-hydroxylase/17,20- lyase (CYP17), which is a crucial enzyme for steroid hormone biosynthesis, is widely used to treat androgen-dependent prostate cancer (PC). CYP17 has dual enzymatic activity: 17alpha-hydroxylase activity (utilizing delta4- C21 steroids as substrates) and the 17,20-lyase activity (using delta5- C21 steroids as substrates). The steroid biosynthetic pathway is directed to either the production of corticosteroids or sex hormones depending on the activity of CYP17. In this review, the current information on the genetics, molecular structure, substrate specificity and inhibitors of CYP17 is analyzed and discussed.

At the crossroads of steroid hormone biosynthesis: the role, substrate specificity and evolutionary development of CYP17.

Cytochrome P450s play critical roles in the metabolism of various bioactive compounds. One of the crucial functions of cytochrome P450s in Chordata is in the biosynthesis of steroid hormones. Steroid 17alpha-hydroxylase/17,20-lyase (CYP17) is localized in endoplasmic reticulum membranes of steroidogenic cells. CYP17 catalyzes the 17alpha-hydroxylation reaction of delta4-C21 steroids (progesterone derivatives) and delta5-C21 steroids (pregnenolone derivatives) as well as the 17,20-lyase reaction producing C19-steroids, a key branch point in steroid hormone biosynthesis. Depending on CYP17 activity, the steroid hormone biosynthesis pathway is directed to either the formation of mineralocorticoids and glucocorticoids or sex hormones. In the present review, the current information on CYP17 is analyzed and discussed.