Affinity-purified melittin antibody recognizes the calmodulin-binding domain on calmodulin target proteins

Identification of a Region of the Polypeptide Chain of Na,K-ATPase α-Subunit Interacting with 67-kDa Melittin-Like Protein

It was shown earlier that a 67-kDa protein purified from mouse kidney using polyclonal antibodies against melittin (a peptide from bee venom) interacted with Na,K-ATPase from rabbit kidney. In this study, a 43-kDa proteolytic fragment of Na,K-ATPase α-subunit interacting with the 67-kDa melittin-like protein was found. The α-subunit was hydrolyzed by trypsin in the presence of 0.5 mM ouabain (E2-conformation of Na,K-ATPase). A proteolytic fragment interacting with the 67-kDa melittin-like protein that was identified by mass-spectrometry is a region of the cytoplasmic domain of Na,K-ATPase α-subunit located between amino acid residues 591 and 775. The fragment includes a conservative DPPRA motif that occurs in many P-type ATPases. It was shown earlier that this motif of H,K-ATPase from gastric mucosa binds to melittin. We suggest that namely this motif of P-type ATPases is able to interact with proteins containing melittin-like modules.

Sequence identity and antigenic cross-reactivity of white face hornet venom allergen, also a hyaluronidase, with other proteins

White face hornet (Dolichovespula maculata) venom has three known protein allergens which induce IgE response in susceptible people. They are antigen 5, phospholipase A1, and hyaluronidase, also known as Dol m 5, 1, and 2, respectively. We have cloned Dol m 2, a protein of 331 residues. When expressed in bacteria, a mixture of recombinant Dol m 2 and its fragments was obtained. The fragments were apparently generated by proteolysis of a Met-Met bond at residue 122, as they were not observed for a Dol m 2 mutant with a Leu-Met bond. Dol m 2 has 56% sequence identity with the honey bee venom allergen hyaluronidase and 27% identity with PH-20, a human sperm protein with hyaluronidase activity. A common feature of hornet venom allergens is their sequence identity with other proteins in our environment. We showed previously the sequence identity of Dol m 5 with a plant protein and a mammalian testis protein and of Dol m 1 with mammalian lipases. In BALB/c mice, Dol m 2 and bee hyaluronidase showed cross-reactivity at both antibody and T cell levels. These findings are relevant to some patients' multiple sensitivity to hornet and bee stings.

Duchenne muscular dystrophy and dystrophin: sequence homology observations

Duchenne muscular dystrophy (DMD) is a genetically transmitted disease characterized by progressive muscle weakness and usually leads to death. DMD results from the absence, deficiency or dysfunction of the protein dystrophin. Analysis of protein data bases, including homology alignments and domain recognition patterns, have located highly significant correlations between dystrophin and other calcium regulating proteins. In particular, a major portion of the dystrophin sequence has been found to contain repeating units of approximately 100 amino acid residues. These repeating units were found to exhibit significant homology to troponin I. Troponin I has been found to bind to the calcium binding proteins calmodulin and troponin C. The regions of highest homology were characterized by patterns of high localization of charged amino acids and thus could represent a possible calmodulin or troponin C surface accessible binding site. Since subcellular localization studies have indicated that dystrophin is associated with the triadic junction, these findings imply that dystrophin could be involved in controlling intracellular calcium homeostasis.

Acyl carrier protein interacts with melittin

Acyl carrier protein (ACP) from Escherichia coli has been shown to form complexes with melittin, a cationic peptide from bee venom. ACP is a small (Mr 8847), acidic, Ca2(+)-binding protein, which possesses some characteristics resembling those of regulatory Ca2(+)-binding proteins including interaction with melittin. Complexing between melittin and ACP which occurred both in the presence and absence of Ca2+ was evident by chemical cross-linking the two peptides, fluorescence changes (including anisotropy measurements), and inhibition by melittin of the activity of a nonaggregated fatty acid synthetase from Euglena. Also, anti-Apis mellifera antibodies which contained antibodies against melittin specifically inhibited the same enzyme system activity relative to non-immune IgG.

Melittin inhibition of the gastric (H+ + K+) ATPase and photoaffinity labeling with [125I]azidosalicylyl melittin

Melittin is a 26-amino acid amphipathic polypeptide toxin from bee venom which forms anion-selective ion channels in bilayers and biological membranes under the influence of membrane potential. Melittin has been shown to interact with a number of membrane proteins. We found that melittin inhibited K+-stimulated ATP hydrolysis by the (H+ + K+) ATPase in parietal cell apical membrane vesicles derived from histamine-stimulated rabbit gastric mucosa with a KIapp of 0.5 micron. Melittin also inhibited K+-stimulated p-nitrophenyl hydrolysis activity which is associated with the gastric (H+ + K+) ATPase in a dose-dependent manner with a KIapp of 0.95 micron. ATP-driven, K+-dependent H+ transport was inhibited over this same concentration range, even in the absence of a membrane potential. Melittin did not appear to increase the H+ leak from vesicle with preformed H+ gradients when the H+ pump was arrested by Mg2+ chelation, but all possible membrane perturbation effects were difficult to rule out. However, the data suggest that melittin exerts its inhibitory effect through interaction with the (H+ + K+) ATPase. In order to determine whether direct interactions between the (H+ + K+) ATPase and melittin occurred, a radioactive derivative of melittin, [125I]azidosalicylyl melittin, was prepared and photoreacted with sealed rabbit gastric membranes and highly purified hog gastric membrane containing the (H+ + K+) ATPase. In the purified hog preparation only a 95,000-Da band, the (H+ + K+) ATPase was labeled, while in the rabbit preparation a 95,000-Da band and one other membrane protein of 70,000 Da were labeled with this reagent. Label incorporation into the (H+ + K+) ATPase and the 70,000-Da band was greatly reduced by addition of excess unlabeled melittin, suggesting specificity of the interaction. Label incorporation occurred in the absence of ATP or added salts and was not reduced by SCH28080 (a K+ site inhibitor) suggesting that the melittin binding site was distinct from the luminal K+ site of action of SCH28080.

Stimulation of enzymatic activity in filament preparations of casein kinase II by polylysine, melittin, and spermine

Casein kinase II (CKII) has been purified from bovine heart tissue. Under conditions of low salt (0.05 M NaCl, 10 mM MgCl2), CKII forms structured aggregates that appear as filaments similar to results obtained with Drosophila CKII [C.V.C. Glover (1986) J. Biol. Chem. 261:14349]. The aggregates have been analyzed by sucrose density gradients and electron microscopy. Filament preparations of the enzyme have reduced but measurable kinase activity. The addition of salt restores activity. Various modulators of CKII activity have been examined with the enzyme in the low salt, polymerized form. The polyamines spermine or spermidine stimulated CKII activity as much as six fold; putrescine had no effect. Polylysine of varying lengths activated CKII 4-6 fold. Melittin, the basic polypeptide from bee venom, was also an effective activator. Activation of filament preparations was also observed if the CKII specific peptide (RRREEETEEE) was used as the substrate in place of casein. These results with filament preparations provide an alternative in vitro system for the study of possible regulatory aspects of CKII.

Properties of a monoclonal antibody directed to the calmodulin-binding domain of rabbit skeletal muscle myosin light chain kinase

A synthetic peptide representing the calmodulin-binding domain of rabbit skeletal muscle myosin light chain kinase (K-R-R-W-K-K-N-F-I-A-V-S-A-A-N-R-F-K-K-I-S-S-S-G-A-L) was used as an antigen to produce a monoclonal antibody. The antibody (designated MAb RSkCBP1, of the IgM class) reacted with similar affinity (KD approximately 20 nM) by competitive enzyme-linked immunoassay (ELISA) with the antigen peptide and intact rabbit skeletal muscle myosin light chain kinase. MAb RSkCBP1 inhibited rabbit skeletal muscle myosin light chain kinase activity competitively with respect to calmodulin (Ki = 20 nM). The antibody also inhibited myosin light chain kinase activity in extracts of skeletal muscle from several mammalian species (rabbit, sheep, and bovine) and an avian species (chicken). The concentration of MAb RSKCBP1 required for 50% inhibition of enzyme activity was similar for the mammalian species (80 nM) but was significantly higher for the avian species (1.2 microM). A competitive ELISA protocol was used to analyze weak cross-reactivity to other calmodulin-binding peptides and proteins. This assay demonstrated no cross-reactivity with the venom peptides melittin or mastoparan; smooth muscle myosin light chain kinases from hog carotid, bovine trachea, or chicken gizzard; bovine brain calmodulin-dependent calcineurin; or rabbit skeletal muscle troponin I. These data support the contention that the synthetic peptide used as the antigen represents the calmodulin-binding domain of rabbit skeletal muscle myosin light chain kinase and that the calmodulin-binding domains of different calmodulin-regulated proteins may have distinct primary and/or higher order structures.