Membrane proteins prostaglandin

Picot, D., Loll, P.J., Garavito, R.M. The x-ray crystal structure of the membrane protein prostaglandin H2 synthase-1. Nature 367 243-249, 1994. 

Despite considerable efforts very few membrane proteins have yielded crystals that diffract x-rays to high resolution. In fact, only about a dozen such proteins are currently known, among which are porins (which are outer membrane proteins from bacteria), the enzymes cytochrome c oxidase and prostaglandin synthase, and the light-harvesting complexes and photosynthetic reaction centers involved in photosynthesis. In contrast, many other membrane proteins have yielded small crystals that diffract poorly, or not at all, using conventional x-ray sources. However, using the most advanced synchrotron sources (see Chapter 18) it is now possible to determine x-ray structures from protein crystals as small as 20 pm wide which will permit more membrane protein structures to be elucidated. 

Effects of acetylcholine, histamine, prostaglandin I2, and E2, and gastrin on gastric acid secretion by the parietal cells of stomach Gs and Gj are membrane proteins that mediate the stimulatory or inhibitory effect of receptor coupling to adenylyl cyclase. 

Step 2- FGJi travels to the nucleus, where it binds to PPAR, followed by binding to RXR. The result is a complex composed of the hormone (PGJ2) and the two prateins (PPAR and RXR). The particular family of receptor proteins that includes FFAR and RXR is water soluble and not membrane bound. Prostaglandin I2 binds to an intracellular receptor (PJ AR), in contrast to other types of prostaglandins that bind to extracellular receptors. 

Glomerular visceral epithelial cells (podocytes) in culture should at least have retained the potency to produce basement membrane constituents (collagen IV and glycosaminoglycans) and maintain the expression of cytokeratin, the membrane proteins megahn and podocalyxin [25], complement C3b and angiotensin II receptors, as well as the synthetic machinery for the synthesis of prostaglandins (Prostaglandin E2 and thromboxane) [26]. 

The monotopic membrane proteins [118], that cross only one bilayer but not two, such as the prostaglandin H2 synthase [119], and self-inserting membrane proteins or toxins [120], such as colicin A [121], diphtheria toxin [122], beetle 6-endotoxin [123] and annexin [124] are associated with poor prediction (not shown). 

More generally, the presence of aromatic residues such as Trp, Phe, and T r near the membrane-solution interface is a recurrent structural feature of several membrane proteins, e.g., bacterial photosynthetic reaction center (PRC), porins, Pfl and fd viral coat proteins, prostaglandin H synthase, the peptide segment of hemmagglutinin responsible for influenza virus fusion, and a large series of a-helical human type I membrane proteins. As an illustration, the GA channel and the PRC are shown in Figure 10. The relative location of the Trp residues in both systems is strikingly similar. 

FIGURE 17 Ribbon representation of selected integral membrane proteins, (a) Photoreaction center, (b) bacterial porin, (c) bacteriorhodopsin, (d) prostaglandin synthase. 

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