N-/C- termini

Fig. 8. Illustration of the actin monomer structure solved by X-ray crystallography (Kabsch et al, 1990) showing the four structural subdomains of the actin monomer, labeled, in the front (A) and back (B) view with N, C-termini labeled 1-4. Also labeled is the loop linking residues 262 and 309 between subdomains 3 and 4.

Several silk fibroin genes have been cloned and sequenced and they all show a similar sequence pattern variable domains at the N- and C-termini flank a large region of repetitive short sequences of alternating poly-Ala (8 to 10 residues) and Gly-Gly-X repeats (where X is usually Ser, Tyr, or Gin). This middle region varies in length and may comprise up to 800 residues. 

Hydrophobicity plots of AQPs indicated that these proteins consist of six transmembrane a-helices (Hl-H6 in Fig. la) connected by five connecting loops (A-E), and flanked by cytosolic N- and C-termini. The second half of the molecule is an evolutionary duplicate and inverse orientation of the first half of the molecule. Loops B and E of the channel bend into the membrane with an a-helical conformation (HB, HE in Fig. lb) and meet and each other at their so-called Asn-Pro-Ala (NPA) boxes. These NPA motifs are the hallmark of AQPs and form the actual selective pore of the channel, as at this location, the diameter is of that of a water molecule (3 A Fig. la and b). Based on the narrowing of the channel from both membrane sides to this small... 

Inward Rectifier K Channels. Figure 4 Kir channel subunits consist of two transmembrane domains (M1, M2), separated by a pore loop (P-loop) that contains the signature K+-selectivity sequence (-GYG-), as well as extended cytoplasmic N - and C-termini. Several residues (indicated) have been implicated in causing rectification (see text). 

The amino acid sequence of our first aPNA (which we termed backbone 1 or bl) was designed based on this amphipathic hehx sequence (Fig. 5.3 B). Specifically, this aPNA backbone included hydrophobic amino acids (Ala and Aib), internal salt bridges (Glu-(aa)3-Lys-(aa)3-Glu), a macrodipole (Asp-(aa)i5-Lys), and an N-ace-tyl cap to favor a-helix formation. The C-termini of these aPNA modules end in a carboxamide function to preclude any potential intramolecular end effects. Each aPNA module incorporates five nucleobases for Watson-Crick base pairing to a target nucleic acid sequence. 

Using the general synthetic concepts described in Sec. II, we employed tyrosine dipeptides as the monomeric starting material. After protection of the N and C termini, the reactivity of a fully protected tyrosine dipeptide (structure 2) could be expected to resemble the... 

By far the most studied family of the G-protein-coupled receptors are the rhodopsin-like receptors. These are also the largest group of receptors in number as they include receptors not only for the monoamines, nucleotides, neuropeptides and peptide hormones, but they also include the odorant receptors which number several hundreds of related receptors. These receptors have short N-termini, a conserved disulphide bridge between the TM2-TM3 and TM4—TM5 extracellular domains, and variable-length C-termini. In some cases the C-terminus is myristolyated which by tying the C-terminus to the cell membrane generates a fourth intracellular loop. 

Figure 8.6 Schematic diagram of the proposed structure of the vesicular monoamine transporter. There are 12 transmembrane segments with both the N- and C-termini projecting towards the neuronal cytosol. (Based on Schuldiner 1998)...

Information about the putative folding of the H,K-ATPase catalytic subunit through the membrane has been obtained by the combined use of hydropathy analysis according to the criteria of Kyte and Doolittle [51], identification of sites sensitive to chemical modification [46,48,50,52-55], and localization of epitopes of monoclonal antibodies [56]. The model of the H,K-ATPase catalytic subunit (Fig. 1) which has emerged from these studies shows ten transmembrane segments and contains cytosolic N- and C-termini [53]. This secondary structure of the catalytic subunit is probably a common feature of the catalytic subunits of P-type ATPases, since evidence supporting a ten a-helical model with cytosolic N- and C-termini has also been published recently for both Ca-ATPase of the sarcoplasmic reticulum and Na,K-ATPase [57-59]. 

In order to identify tyrosine derivatives that would lead to polymers that are processible, mechanically strong, and also biocompatible, we initiated a detailed investigation of the structure-property relationships in polyiminocarbonates and polycarbonates. Since the amino and carboxylic acid groups of tyrosine dipeptide (the N and C termini) provide convenient attachment points, selected pendent chains can be used to modify the overall properties of the polymers. This is an important structural feature of tyrosine dipcptide derived polymers. 

The receptors range in size from 379 to 595 amino acids. The receptors have two transmembrane regions with intracellular N- and C-termini (Figure 3.11). Extensive SCAM analysis suggests that TM2 forms the pore, and a conserved glycine residue in the middle of TM2 lines the narrowest part of the channel. The structure of the pore and the location of the gate have still not been... 

Figure 7.2 (a) Schematic representation of the structure of B. subtilis ferrochelatase. Domain I is coloured green and domain II blue. The parts of the chain in red build up the walls of the cleft, and the region in yellow makes the connection between the domains. The N- and C-termini are marked, (b) The proposed active site of ferrochelatase with protoporphyrin IX molecule (red) modelled into the site. The backbone atoms of the protein are in purple, the side-chains in blue. Reprinted from Al-Karadaghi et ah, 1997. Copyright (1997), with permission from Elsevier Science. 

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