Inflammation-Associated Nitrotyrosination Affects TCR Recognition through Reduced Stability and Alteration of the Molecular Surface of the MHC Complex

Nitrotyrosination of proteins, a hallmark of inflammation, may result in the production of MHC-restricted neoantigens that can be recognized by T cells and bypass the constraints of immunological self-tolerance. Here we biochemically and structurally assessed how nitrotyrosination of the lymphocytic choriomeningitis virus (LCMV)-associated immunodominant MHC class I-restricted epitopes gp33 and gp34 alters T cell recognition in the context of both H-2Db and H-2Kb. Comparative analysis of the crystal structures of H-2Kb/gp34 and H-2Kb/NY-gp34 demonstrated that nitrotyrosination of p3Y in gp34 abrogates a hydrogen bond interaction formed with the H-2Kb residue E152. As a consequence the conformation of the TCR-interacting E152 was profoundly altered in H-2Kb/NY-gp34 when compared to H-2Kb/gp34, thereby modifying the surface of the nitrotyrosinated MHC complex. Furthermore, nitrotyrosination of gp34 resulted in structural over-packing, straining the overall conformation and considerably reducing the stability of the H-2Kb/NY-gp34 MHC complex when compared to H-2Kb/gp34. Our structural analysis also indicates that nitrotyrosination of the main TCR-interacting residue p4Y in gp33 abrogates recognition of H-2Db/gp33-NY complexes by H-2Db/gp33-specific T cells through sterical hindrance. In conclusion, this study provides the first structural and biochemical evidence for how MHC class I-restricted nitrotyrosinated neoantigens may enable viral escape and break immune tolerance

Structures of designed armadillo-repeat proteins show propagation of inter-repeat interface effects

The armadillo repeat serves as a scaffold for the development of modular peptide-recognition modules. In order to develop such a system, three crystal structures of designed armadillo-repeat proteins with third-generation N-caps (YIII-type), four or five internal repeats (M-type) and second-generation C-caps (AII-type) were determined at 1.8 Å (His-YIIIM4AII), 2.0 Å (His-YIIIM5AII) and 1.95 Å (YIIIM5AII) resolution and compared with those of variants with third-generation C-caps. All constructs are full consensus designs in which the internal repeats have exactly the same sequence, and hence identical conformations of the internal repeats are expected. The N-cap and internal repeats M1 to M3 are indeed extremely similar, but the comparison reveals structural differences in internal repeats M4 and M5 and the C-cap. These differences are caused by long-range effects of the C-cap, contacting molecules in the crystal, and the intrinsic design of the repeat. Unfortunately, the rigid-body movement of the C-terminal part impairs the regular arrangement of internal repeats that forms the putative peptide-binding site. The second-generation C-cap improves the packing of buried residues and thereby the stability of the protein. These considerations are useful for future improvements of an armadillo-repeat-based peptide-recognition system

Crystal structures of designed armadillo repeat proteins: Implications of construct design and crystallization conditions on overall structure

Designed armadillo repeat proteins (dArmRP) are promising modular proteins for the engineering of binding molecules that recognize extended polypeptide chains. We determined the structure of a dArmRP containing five internal repeats and 3rd generation capping repeats in three different states by X-ray crystallography: without N-terminal His6 -tag and in the presence of calcium (YM5 A/Ca(2+) ), without N-terminal His6 -tag and in the absence of calcium (YM5 A), and with N-terminal His6 -tag and in the presence of calcium (His-YM5 A/Ca(2+) ). All structures show different quaternary structures and superhelical parameters. His-YM5 A/Ca(2+) forms a crystallographic dimer, which is bridged by the His6 -tag, YM5 A/Ca(2+) forms a domain-swapped tetramer, and only in the absence of calcium and the His6 -tag, YM5 A forms a monomer. The changes of superhelical parameters are a consequence of calcium binding, because calcium ions interact with negatively charged residues, which can also participate in the modulation of helix dipole moments between adjacent repeats. These observations are important for further optimizations of dArmRPs and provide a general illustration of how construct design and crystallization conditions can influence the exact structure of the investigated protein

Indigenous craft and gears used for crab fishery in Cochin estuary, Kerala, southwest coast of India

This paper presents an overview of fishing gears and crafts operated for crab fishery in the Cochin estuary. A survey was made in selected areas of the Cochin estuary to study the design and operational details of indigenous craft and gears used in crab fishing. Primary data on crab fishery were collected from fish landing centers and fishing villages through a structured questionnaire. Crab gillnets and ring nets are the dominant artisanal gear supporting crab fishery throughout the study area. Long lines were one of the widely deployed fishing gears for the crab fishery, which is now operational only in limited areas of the Cochin estuary. Incidental catch of crabs is also noted in the stake net and Chinese dip net. The wounding gears and traditional fishing techniques, viz., vazhuka method and midrib trap, are not deployed in commercial crab fishery as they result in low-value realization. The survey discloses that ring net and crab gillnet accounted for 98% of the crab landing along the Cochin estuary. Scylla serrata and Scylla olivacea are the essential species contributing to inland crab fishery along the study area. Wooden canoes belonging to 3 to 7 m in length overall (LOA) are employed for crab fishing. Migrant fishermen use Coracles and the FRP canoes for crab gill net operations along the stretches of the backwaters.

Structures of designed armadillo repeat proteins binding to peptides fused to globular domains

Designed armadillo repeat proteins (dArmRP) are α-helical solenoid repeat proteins with an extended peptide binding groove that were engineered to develop a generic modular technology for peptide recognition. In this context, the term "peptide" not only denotes a short unstructured chain of amino acids, but also an unstructured region of a protein, as they occur in termini, loops, or linkers between folded domains. Here we report two crystal structures of dArmRPs, in complex with peptides fused either to the N-terminus of Green Fluorescent Protein or to the C-terminus of a phage lambda protein D. These structures demonstrate that dArmRPs bind unfolded peptides in the intended conformation also when they constitute unstructured parts of folded proteins, which greatly expands possible applications of the dArmRP technology. Nonetheless, the structures do not fully reflect the binding behavior in solution, that is, some binding sites remain unoccupied in the crystal and even unexpected peptide residues appear to be bound. We show how these differences can be explained by restrictions of the crystal lattice or the composition of the crystallization solution. This illustrates that crystal structures have to be interpreted with caution when protein-peptide interactions are characterized, and should always be correlated with measurements in solution

Structure and Energetic Contributions of a Designed Modular Peptide-Binding Protein with Picomolar Affinity

Natural armadillo repeat proteins (nArmRP) like importin-α or β-catenin bind their target peptides such that each repeat interacts with a dipeptide unit within the stretched target peptide. However, this modularity is imperfect and also restricted to short peptide stretches of usually four to six consecutive amino acids. Here we report the development and characterization of a regularized and truly modular peptide-specific binding protein, based on designed armadillo repeat proteins (dArmRP), binding to peptides of alternating lysine and arginine residues (KR)n. dArmRP were obtained from nArmRP through cycles of extensive protein engineering, which rendered them more uniform. This regularity is reflected in the consistent binding of dArmRP to (KR)-peptides, where affinities depend on the lengths of target peptides and the number of internal repeats in a very systematic manner, thus confirming the modularity of the interaction. This exponential dependency between affinity and recognition length suggests that each module adds a constant increment of binding energy to sequence-specific recognition. This relationship was confirmed by comprehensive mutagenesis studies that also reveal the importance of individual peptide side chains. The 1.83 Å resolution crystal structure of a dArmRP with five identical internal repeats in complex with the cognate (KR)5 peptide proves a modular binding mode, where each dipeptide is recognized by one internal repeat. The confirmation of this true modularity over longer peptide stretches lays the ground for the design of binders with different specificities and tailored affinities by the assembly of dipeptide-specific modules based on armadillo repeats

Two isoforms of anti-lipopolysaccharide factors identified and characterized from the hemocytes of portunid crabs, Portunus pelagicus and Scylla tranquebarica

Anti-lipopolysaccharide factors (ALFs), a type of cationic antimicrobial peptides (AMPs), and their derivatives are becoming predominant candidates for potential drugs in viral and bacterial diseases. This study reports the first ALF from the mud crab Scylla tranquebarica (StALF, JQ899453) and the second ALF isoform from the blue swimmer crab Portunus pelagicus (PpALF2, JQ899452). Both sequences encoded for precursor molecules, starting with a signal peptide containing 26 amino acid residues, followed by a highly cationic mature peptide, containing two conserved cysteine residues flanking a putative lipopolysaccharide (LPS)-binding domain. BLAST analysis revealed that both PpALF2 and StALF exhibited significant similarity with crustacean ALF sequences. The predicted molecular mass of the mature ALFs was 11.2 kDa with an estimated pI of 10.0. PpALF2 and StALF also showed the typical pattern of alternating hydrophobic and hydrophilic residues in their putative disulphide loop, suggesting that they comprise the same functional domain. Phylogenetic analysis showed that PpALF2 and StALF have similar evolutionary status and they were phylogenetically ancient immune effector molecules which may play an essential role in the host defense mechanism. The spatial structures of PpALF2 and StALF possessed four beta-strands and two alpha-helices. The results indicated that there were more than one ALF involved in crab immunity against various pathogens. ALFs would provide candidate promising therapeutic or prophylactic agents in health management and diseases control in crustacean aquacultureCochin University Of Science And TechnologyMolecular Immunology 52 (2012) 258– 26

Molecular Characterisation and Phylogenetic Analysis of a Novel Isoform of Hepatic Antimicrobial Peptide, Hepcidin (Zc-hepc1), from the Coral Fish Moorish idol, Zanclus cornutus (Linnaeus,1758)

Hepcidin is a family of short cysteine-rich antimicrobial peptides (AMPs) participating in various physiological functions with inevitable role in host immune responses. Present study deals with identification and characterisation of a novel hepcidin isoform from coral fish Zanclus cornutus. The 81 amino acid (aa) preprohepcidin obtained from Z. cornutus consists of a hydrophobic aa rich 22 mer signal peptide, a highly variable proregion of 35 aa and a bioactive mature peptide with 8 conserved cysteine residues which contribute to the disulphide back bone. The mature hepcidin, Zc-hepc1 has a theoretical isoelectric point of 7.46, a predicted molecular weight of 2.43 kDa and a net positive charge of ?1. Phylogenetic analysis grouped Z. cornutus hepcidin with HAMP2 group hepcidins confirming the divergent evolution of hepcidin-like peptide in fishes. Zc-hepc1 can attain a b-hairpin-like structure with two antiparallel b-sheets. This is the first report of an AMP from the coral fish Z. cornutus.Cochin University of Science and TechnologyProbiotics & Antimicro. Prot. (2013) 5:187–194 DOI 10.1007/s12602-013-9139-

Characterization of Histone H2A Derived Antimicrobial Peptides, Harriottins, from Sicklefin Chimaera Neoharriotta pinnata (Schnakenbeck, 1931) and Its Evolutionary Divergence with respect to CO1 and Histone H2A

Antimicrobial peptides (AMPs) are humoral innate immune components of fishes that provide protection against pathogenic infections. Histone derived antimicrobial peptides are reported to actively participate in the immune defenses of fishes. Present study deals with identification of putative antimicrobial sequences from the histone H2A of sicklefin chimaera, Neoharriotta pinnata. A 52 amino acid residue termed Harriottin-1, a 40 amino acid Harriottin-2, and a 21 mer Harriottin-3 were identified to possess antimicrobial sequence motif. Physicochemical properties andmolecular structure ofHarriottins are in agreement with the characteristic features of antimicrobial peptides, indicating its potential role in innate immunity of sicklefin chimaera. The histone H2A sequence of sicklefin chimera was found to differ from previously reported histone H2A sequences. Phylogenetic analysis based on histone H2A and cytochrome oxidase subunit-1 (CO1) gene revealed N. pinnata to occupy an intermediate position with respect to invertebrates and vertebratesCochin University of Science and TechnologyISRN Molecular Biology Volume 2013, Article ID 930216, 10 page