Characterization of tail sheath protein of giant bacteriophage phiKZ Pseudomonas aeruginosa.

AbstractThe tail sheath protein of giant bacteriophage φKZ Pseudomonas aeruginosa encoded by gene 29 was identified and its expression system was developed. Localization of the protein on the virion was confirmed by immunoelectron microscopy. Properties of gene product (gp) 29 were studied by electron microscopy, immunoblotting and limited trypsinolysis. Recombinant gp29 assembles into the regular tubular structures (polysheaths) of variable length. Trypsin digestion of gp29 within polysheaths or extended sheath of virion results in specific cleavage of the peptide bond between Arg135 and Asp136. However, this cleavage does not affect polymeric structure of polysheaths, sheaths and viral infectivity. Digestion by trypsin of the C-truncated gp29 mutant, lacking the ability to self-assemble, results in formation of a stable protease-resistant fragment. Although there is no sequence homology of φKZ proteins to proteins of other bacteriophages, some characteristic biochemical properties of gp29 revealed similarities to the tail sheath protein of bacteriophage T4

Modular toxin from the lynx spider Oxyopes takobius: Structure of spiderine domains in solution and membrane-mimicking environment.

We have recently demonstrated that a common phenomenon in evolution of spider venom composition is the emergence of so‐called modular toxins consisting of two domains, each corresponding to a “usual” single‐domain toxin. In this article, we describe the structure of two domains that build up a modular toxin named spiderine or OtTx1a from the venom of Oxyopes takobius. Both domains were investigated by solution NMR in water and detergent micelles used to mimic membrane environment. The N‐terminal spiderine domain OtTx1a‐AMP (41 amino acid residues) contains no cysteines. It is disordered in aqueous solution but in micelles, it assumes a stable amphiphilic structure consisting of two α‐helices separated by a flexible linker. On the contrary, the C‐terminal domain OtTx1a‐ICK (59 residues) is a disulfide‐rich polypeptide reticulated by five S–S bridges. It presents a stable structure in water and its core is the inhibitor cystine knot (ICK) or knottin motif that is common among single‐domain neurotoxins. OtTx1a‐ICK structure is the first knottin with five disulfide bridges and it represents a good reference for the whole oxytoxin family. The affinity of both domains to membranes was measured with NMR using titration by liposome suspensions. In agreement with biological tests, OtTx1a‐AMP was found to show high membrane affinity explaining its potent antimicrobial properties