Hydrophobic faces

The structure of cholic acid helps us understand how bile salts such as sodium tauro cholate promote the transport of lipids through a water rich environment The bot tom face of the molecule bears all of the polar groups and the top face is exclusively hydrocarbon like Bile salts emulsify fats by forming micelles m which the fats are on the inside and the bile salts are on the outside The hydrophobic face of the bile salt associates with the fat that is inside the micelle the hydrophilic face is m contact with water on the outside... 

P Sheets can also have a hydrophobic face and a hydrophilic face. The backbone of the p sheet is arranged so that every other side chain points to the same side of the sheet. If the primary sequence alternates hydrophobic-hydrophilic, one surface of the sheet will be hydrophobic and the other will be hydrophilic. 

Figure 2 shows FFEM images of Mal3 (Phyt)2/SQDG (9 1 mol/mol) vesicle membranes in the presence (Fig. 2A, B) or in the absence (Fig. 2C, D) of BR. Small particles were observed in Figure 2A, B, whereas no such particles were observed for pure Mai (Phyt)2/SQDG vesicles. In addition, two fracture faces of the bilayer membranes, a convex surface (a hydrophobic face of an inner leaflet, Fig. 2A) and a concave surface (a hydrophobic face of an outer leaflet, Fig. 2B) exhibited intramembraneous particles, suggesting BR was incorporated into vesicles transmembraneously.

An alternative efficient approach to disperse CNTs relies on the use of synthetic peptides. Peptides were designed to coat and solubilise the CNTs by exploiting a noncovalent interaction between the hydrophobic face of amphiphilic helical peptides and the graphitic surface of CNTs (Dieckmann et al., 2003 Zoibas et al., 2004 Dalton et al., 2004 Arnold et al., 2005). Peptides showed also selective affinity for CNTs and therefore may provide them with specifically labelled chemical handles (Wang et al., 2003). Other biomolecules, such as Gum Arabic (GA) (Bandyopadhyaya et al., 2002), salmon sperm DNA, chondroitin sulphate sodium salt and chitosan (Zhang et al., 2004 Moulton et al., 2005), were selected as surfactants to disperse CNTs (Scheme 2.1). 

While functional (immunological) mimicry has been established, the basis of mimicry on the molecular level remains to be explained. Several hypotheses have been put forward one of the earliest was that the side chains of aromatic amino acid residues might mimic the hydrophobic faces of the pyranosyl rings of carbohydrates. Before 1997, no structural evidence was available to support or discount these hypotheses. The nature of peptide-carbohydrate mimicry on the molecular level became the subject of structural investigations, and the resulting studies along with functional data will be discussed below. 

While these complex model heme proteins have a large potential for functionalization, an interesting approach that is very different has been taken by other workers in that the heme itself functions as the template in the formation of folded peptides. In these models peptide-peptide interactions are minimized and the driving force for folding appears to be the interactions between porphyrin and the hydrophobic faces of the amphiphiUc peptides. The amino acid sequences are too small to permit peptide-peptide contacts as they are separated by the tetrapyrrole residue. These peptide heme conjugates show well-re-solved NMR spectra and thus well-defined folds and the relationship between structure and function can probably be determined in great detail when functions have been demonstrated [22,23,77]. They are therefore important model systems that complement the more complex proteins described above. 

Fig. 5. Two different views (ca. 180°) of a single tricolorin A (106) molecule. Left, hydrophilic face. Right, hydrophobic face. Protons of hydroxyl groups are colored in cyan...

In contrast to azurin, the plant plastocyanins have a conserved negative patch of residues adjacent to a putative redox partner-binding site. Plastocyanin has, in addition, the hydrophobic face into which the edge of the second histidine ligand is inserted. 

The salient features of A. faecalis pseudoazurin are that (1) it has a Cu-Met bond length shorter than that of either plastocyanin or azurin (see Table III) (2) it has only one NH - S bond, as does plastocyanin and (3) its overall architecture resembles plastocyanin (see Fig. 4), with an extended carboxy terminus folded into two a helices [a preliminary sequence comparison suggested that the folding would resemble plastocyanin (Adman, 1985)]. It retains the exposed hydrophobic face found in azurin and plastocyanin. Just how it interacts with nitrite reductase is still a subject of investigation. It is intriguing that the carboxy-terminal portion folds up onto the face of the molecule where the unique portions of other blue proteins are the flap in azurin, and, as we see below in the multi-copper oxidase, entire domains. 

Due possibly to the above mentioned heterogeneity, there is some variability with regard to the conclusions reached by various workers concerning the structure and configuration of bovine serum albumin. Brown (1977) proposed two possible models based on the primary sequence of the protein. He demonstrated that the molecule could possess a triple domain structure with three very similar domains residues 1-190, 191-382, and 383-582. Each domain could then consist of five helical rods of about equal length arranged either in a parallel or an antiparallel manner. His second model consisted of the following (1) a lone subdomain (1-101) (2) a pair of antiparallel subdomains, with their hydrophobic faces toward each other (113-287) (3) another pair of subdomains (314-484) and (4) a lone subdomain (512-582). These structures are supported by the observed helical content of bovine... 

Scheme 1 The Amino Acid Sequences of Designed Amphipathic cx-Helical Peptides with Wide and Narrow Hydrophobic Faces[15labc...

What distinguishes coiled coils from multiple-helix bundles is that coiled coils contain a narrow hydrophobic face on the surface of each a-helix from the 3-4 hydrophobic repeat, whereas in multiple-helix bundles the hydrophobic interface can contain a wider hydro-phobic surface involving hydrophobes additional to the 3-4 repeat (Scheme 1 for a review, see retf22 ). The wider hydrophobic surface will change the hydrophobic packing and relative orientation of the a-helical chains with respect to each other in bundles as opposed to coiled coils.[17 ... 

Shown in the upper panel of Scheme 2 is the top view of the GS14 backbone showing the positions of potential H-bonds (dashed lines) in each five-residue p-strand and the two type II p-turns defined by the D-Tyr-Pro sequence which link the two P-strands. The side view of GS14 (2) is shown in the lower panel of Scheme 2 where the P-sheet structure of the backbone is evident and the relative orientation of successive side chains within the 3-strands can be seen. The P-sheet structure gives GS14 (2) a highly amphipathic nature with a large hydrophobic face made up of Val and Leu residues and a basic face made up of Lys residues. 

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