The tertiary structure for the region 1-63 of the 74 amino acid human complement protein C5a in solution was calculated from a large number of distance constraints derived from nuclear Overhauser effects with an angular distance geometry algorithm. The protein consists of four helices juxtaposed in an approximately antiparallel topology connected by peptide loops located at the surface of the molecule. The structures obtained for the helices are compatible with alpha-helical hydrogen-bonding patterns, which provides an explanation for the observed slow solvent exchange kinetics of the amide protons in these peptide regions. In contrast to the peptide region 1-63, no defined structure could be assigned to the C-terminal region 64-74, which increasingly acquires dynamic random coil characteristics as the end of the peptide chain is approached. An average root-mean-square deviation of 1.6 A was obtained for the alpha-carbons of the first 63 residues in the calculated ensemble of C5a structures, while the alpha-helices were determined with an average root-mean-square deviation of 0.8 A for the alpha-carbons. A comparison between the solution structure of C5a and the crystal structure of the functionally related C3a protein, as well as inferences for the interaction of C5a with its receptor on polymorphonuclear leukocytes, is discussed.
"The tertiary structure of hC5a has been solved by means of nuclear magnetic resonance spectroscopy   . However, the structure of hRP S19 has not yet been reported, although the crystal structure of Pyrococcus abyssi RP S19 was recently solved by Gregory et al. . "
[Show abstract][Hide abstract] ABSTRACT: The crosslinked homodimer of human ribosomal protein S19 (hRP S19) but not hRP S19 monomer shares the hC5a receptor ligation capacity with anaphylatoxin hC5a. The hRP S19 dimer engages hC5a receptor-bearing monocytes in chemotactic movement and secretion as does hC5a. Two submolecular regions essential for the receptor ligation were already identified in hRP S19 as well as in hC5a. Using the tertiary structure data base of an archaeobacterial RP S19 as template, we made a tertiary structure model of hRP S19. The obtained structure was almost entirely α-helical with two short β-sheet regions, and folds a five α-helix bundle organized around a central amphipathic α-helix. While the secondary structure components were similar to those of hC5a, the gross tertiary structure of hRP S19 was loose and the distance between the two receptor binding regions was rather big in comparison to that of hC5a. Anti-recombinant hC5a rabbit antibodies cross-recognized not only the crosslinked hRP S19 dimer but also the guinea pig (gp) RP S19 dimer, however, these antibodies reacted hRP S19 monomer and crosslinked Gln137Asn-hRP S19 mutant dimer at significantly less extents. These antibodies neutralized the monocyte attracting capacity of the hRP S19 dimer in vitro and that of the gpRP S19 dimer in vivo. We assume that the crosslinkage between Lys122 of one hRP S19 molecule and Gln137 of the other one would assemble the hC5a-like structure probably providing one of two receptor binding regions by each hRP S19 subunit.
International immunopharmacology 12/2010; 10(12):1541-7. DOI:10.1016/j.intimp.2010.09.002 · 2.47 Impact Factor
"Previously, only limited information was available on the domain organization of proteins from the C3/␣2-macroglobulin family. Four structural elements of C3 or homologous proteins were known a priori: (i) the anaphylatoxin domain C3a (Huber et al., 1980) and C5a (Zuiderweg et al., 1989), (ii) the fragment C3d and its homologue C4d, which correspond to the thioester-containing domain of C3 and C4 (Nagar et al., 1998; van den Elsen et al., 2002; Zanotti et al., 2000), as well as C3d in complex with the CCP1-2 construct of complement receptor 2 (CR2) (Szakonyi et al., 2001), (iii) the receptor-binding domain (RBD) of ␣2-macroglobulin (␣2M) (Jenner et al., 1998), and (iv) the C-terminal C345c domain of C5 (Bramham et al., 2005). For the remainder (∼60%) of the molecule, most sequence databases listed two large domains, denoted ␣2M N for the N-terminal part and ␣2M for the Cterminal part (the latter included the region corresponding to the RBD domain in ␣2M). "
[Show abstract][Hide abstract] ABSTRACT: Since the resolution of the first three-dimensional structure of a complement component in 1980, considerable efforts have been put into the investigation of this system through structural biology techniques, resulting in about a hundred structures deposited in the Protein Data Bank by the beginning of 2007. By revealing its mechanisms at the atomic level, these approaches significantly improve our understanding of complement, opening the way to the rational design of specific inhibitors. This review is co-authored by some of the researchers currently involved in the structural biology of complement and its purpose is to illustrate, through representative examples, how X-ray crystallography and NMR techniques help us decipher the many sophisticated mechanisms that underlie complement functions.
"Details of the interactions between C3/C4/C5 family members remain undefined, and only a few small, independently folding domains within C5 have been described. These include NMR solution structures for the C5a fragment (8 kDa),24,25 and for the 17 kDa C-terminal C345C domain of the α chain of C5b (cyan in Figure 4(c)).26 The C345C domain of C5 appears to be multifunctional, with roles in both C5 cleavage and MAC assembly.27,28 "
[Show abstract][Hide abstract] ABSTRACT: The complement (C) system is a potent innate immune defence system against parasites. We have recently characterised and expressed OmCI, a 16 kDa protein derived from the soft tick Ornithodoros moubata that specifically binds C5, thereby preventing C activation. The structure of recombinant OmCI determined at 1.9 A resolution confirms a lipocalin fold and reveals that the protein binds a fatty acid derivative that we have identified by mass spectrometry as ricinoleic acid. We propose that OmCI could sequester one of the fatty acid-derived inflammatory modulators from the host plasma, thereby interfering with the host inflammatory response to the tick bite. Mapping of sequence differences between OmCI and other tick lipocalins with different functions, combined with biochemical investigations of OmCI activity, supports the hypothesis that OmCI acts by preventing interaction with the C5 convertase, rather than by blocking the C5a cleavage site.
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