Loops hormone receptor

Figure 13.23 The F-G loop in the C-terminal domain of the prolactin receptor is involved in a unique interaction, (a) The F-G loop of the growth hormone receptor (blue) is not involved in any specific interactions with the growth hormone (red), (b) The F-G loop in the prolactin receptor forms a strong zinc-binding site that links the receptor (green) to the hormone (red). (Adapted from W. Somers et at.. Nature 372 478-481, 1994.)...

Kleinau G, Claus M, Jaeschke H et al (2007) Contacts between extracellular loop two and transmembrane helix six determine basal and hormone induced activity of the thyroid stimulating hormone receptor. J Biol Chem 282(1 ) 518-25... 

The DNA-binding of the steroid hormone receptor occurs via an approx. 60 amino acid DNA-binding domain with two zmc-Cys4-motrfs (see also 4.3.2). The structure displays two so-called helix-loop-hehx elements, each with a boimd Zn ion (Fig. 1.6). 

Integral membrane proteins. Membrane proteins are hard to crystallize178 and precise structures are known for only a few of them.179-181 A large fraction of all of the integral membrane proteins contain one or more membrane-spanning helices with loops of peptide chain between them. Folded domains in the cytoplasm or on the external membrane surface may also be present. The best-known structure of a transmembrane protein is that of the 248-residue bacteriorhodopsin. It consists of seven helical segments that span the plasma membrane (Fig. 23-45) and serves as a light-activated proton pump. Other proteins with similar structures act as hormone receptors in eukaryotic membranes. A seven-helix protein embedded in a membrane is depicted in Fig. 8-5 and also, in more detail, in Fig. 11-6. 

Kudo, M., Osuga, Y., Kobilka, B. K., and Hsueh, A. J. W. (1996). Transmembrane regions V and VI of the human luteinizing hormone receptor are required for constitutive activation by a mutation in the third intracellular loop. / Biol. Chem. 271, 22470-22478. 

Many diuretic agents (loop diuretics, thiazides, amiloride, and triamterene) exert their effects on specific membrane transport proteins in renal tubular epithelial cells. Other diuretics exert osmotic effects that prevent water reabsorption (mannitol), inhibit enzymes (acetazolamide), or interfere with hormone receptors in renal epithelial cells (spironolactone). 

Figure 31.24. Coactivator Structure. The pi60 family of coactivators includes a number of domains that can be recognized at the amino acid sequence level, including a basic helix-loop-helix domain that takes part in DNA binding, a PAS domain that participates in protein-protein interactions, a central domain that contacts the ligandbinding domain of the nuclear hormone receptors, and a domain that interacts with additional coactivators such as p300 and CREB-binding protein (CBP). (CREB stands for cyclic AMP-response element binding protein.) The nuclear hormone receptor interaction domain includes three Leu-X-X-Leu-Leu sequences.

Figure 7. A schematic diagram of the proposed ligand binding domains, shown in light grey, in various GPCRs. The helices are shown as cylinders, the loops, N-termini and C-termini are shown as lines. (A) Biogenic amine receptors, (B) Peptide receptors, (C) Glycoprotein hormone receptors, (D) Thrombin receptor.

In the G protein s unactivated state, the guanyl nucleotide bound to the G protein is GDP. In this form, the G protein exists as a heterotrimer consisting of a, p, and y subunits the ct subunit (referred to as G ) binds the nucleotide (Figure 14.6). The a subunit is a member of the P-loop NTPase family (Section 9.4), and the P-loop participates in nucleotide binding. The a and y subunits are usually anchored to the membrane by covalently attached fatty acids. The role of the hormone-hound receptor is to catalyze the exchange of GTP for hound GDP. The hormone—receptor complex interacts with the heterotrimeric G protein and opens the nucleotide-hinding site... 

---