Structure polypeptide backbone

M Claessens, EV Cutsem, I Lasters, S Wodak. Modelling the polypeptide backbone with spare parts from known protein structures. Protein Eng 4 335-345, 1989. 

FIGURE 5.8 Two structural motifs that arrange the primary structure of proteins into a higher level of organization predominate in proteins the a-helix and the /3-pleated strand. Atomic representations of these secondary structures are shown here, along with the symbols used by structural chemists to represent them the flat, helical ribbon for the a-helix and the flat, wide arrow for /3-structures. Both of these structures owe their stability to the formation of hydrogen bonds between N—H and 0=C functions along the polypeptide backbone (see Chapter 6). 

Whereas the primary structure of a protein is determined by the covalently linked amino acid residues in the polypeptide backbone, secondary and higher... 

Figure 5.12 Structures and nomenclature of the ions formed in the mass spectral fragmentation of peptides which involve scission of the polypeptide backbone. From Chapman, J. R. (Ed.), Protein and Peptide Analysis by Mass Spectrometry, Methods in Molecular Biology, Vol. 61, 1996. Reproduced by permission of Humana Press, Inc.

Figure 52-6. Diagrammatic representation of the structures of the H, A,and B blood group substances. R represents a long complex oligosaccharide chain, joined either to ceramide where the substances are glycosphingolipids, or to the polypeptide backbone of a protein via a serine or threonine residue where the substances are glycoproteins. Note that the blood group substances are biantenna ry ie, they have two arms, formed at a branch point (not indicated) between the GIcNAc—R, and only one arm of the branch is shown. Thus, the H, A,and B substances each contain two of their respective short oligosaccharide chains shown above. The AB substance contains one type A chain and one type B chain.

Figure 1. The three-dimensional structure of PelC. A. A schematic diagram illustrating the major secondary structural features of the PelC polypeptide backbone. The three parallel p sheets are represented by arrows in light, medium and dark gray.

P Turn A structure in which the polypeptide backbone folds back on itself. Turns are useful for connecting helices and sheets. 

Figure 7. Traces of the a-carbon polypeptide backbone of domains 1 and 6 in the hCP structure. Domain 1 is shown (shaded) on the left hand side of the diagram this domain contributes four histidine residues (not shown) to the trinuclear cluster copper atoms are depicted as black spheres. Domain 6 is on the right hand side of the figure and also contributes four histidine residues to the cluster. The portion of the polypeptide chain colored black is that which is missing in the truncated enzyme. This polypeptide, residues 991 to 1046 inclusive, includes two histidine residues bound to the trinuclear copper center and three residues bound to the mononuclear copper in domain 6 these residues are depicted in black. The absence of the C-terminal polypeptide would also remove over 50% of the interdomain hydrogen-bond and iron-pair interactions observed in the intact enzyme.

Figure 1. The structure of NiFe hydrogenases. The large subunit polypeptide (backbone is indicated in grey) harbours the unique NiFe active centre, the small subunit polypeptide (backbone is indicated in dark grey) contains the Fe4S4 clusters for the transfer of electrons between the protein surface and the NiFe centre.

Fig. 2. Ball-and-stick representations of two differently oriented asparagine ladders of (A) W-arcade taken from the crystal structures of pectate lyase C (Lietzke et al., 1996) and (b) ppl-arcade taken from l DP-.V-aretylglucosamine acyltransferase (Raetz and Roderick, 1995). b, l, and so on refer to a one-letter conformational code (Fig. IOC). The ladders are viewed from within the respective /(-solenoids. The arrow shows the orientation (N- to C-terminal) of the solenoid. Oxygen atoms are in red, nitrogen in blue, and carbon in green. Dotted lines designate H-bonds of side chains (red) and inter-coil H-bonds of the polypeptide backbone (black). Except for the ladder-forming asparagines, only the backbones of the coils are shown. Panels are reprinted from Hennetin et al. (2006) with the permission of the publisher.

The association of secondary structures to give super-secondary structures, which frequently constitute compactly folded domains in globular proteins, is completed by the a-a motifs in which two a-helices are packed in an anti-parallel fashion, with a short connecting loop (Figure 4.8c). Examples of these three structural domains, often referred to as folds, are illustrated in Figures 4.9—4.11. The schematic representation of the main chains of proteins, introduced by Jane Richardson, is used with the polypeptide backbone... 

Fig. 1. Schematic drawing of the polypeptide backbone of ribonuclease S (bovine pancreatic ribonuclease A cleaved by subtilisin between residues 20 and 21). Spiral ribbons represent a-helices and arrows represent strands of /3 sheet. The S peptide (residues 1-20) runs down across the back of the structure.

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