China
Africa
Explore chapters and articles related to this topic
Biting insect and tick allergens
Published in Richard F. Lockey, Dennis K. Ledford, Allergens and Allergen Immunotherapy, 2020
Donald R. Hoffman, Jennifer E. Fergeson
The major salivary anticoagulant proteins of Rhodnius prolixus are called prolixins and consist of four related nitrophorin molecules [40], which are heme proteins that carry nitric oxide. The major component has a molecular weight of 19.69 kDa and inhibits factor VIII–mediated activation of factor X. Two proteins are characterized from the saliva of Triatoma pallipidipennis, triabin of 15.62 kDa, an inhibitor of thrombin-based hydrolysis of fibrinogen [41], and pallidipin of 19 kDa, an inhibitor of collagen-induced platelet aggregation [42]. Functional studies of coagulation inhibition suggest that different species of Triatominae have functionally different mechanisms of coagulation inhibition and different sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) profiles of salivary proteins [43,46]. These proteins, along with proteins having histamine binding, platelet inhibition, anticoagulation, and nitric oxide transport activities, are all members of the lipocalin family [44]. The three-dimensional structures of the nitrophorins NP1, 2, and 4 have been determined by x-ray crystallography. Many important vertebrate-derived allergens are also members of the lipocalin family. An activatable serine protease of 40 kDa named triapsin, with an arginine specificity, has been isolated from saliva of Triatoma infestans [45].
Biting Insect and Tick Allergens
Published in Richard F. Lockey, Dennis K. Ledford, Allergens and Allergen Immunotherapy, 2014
The major salivary anticoagulant proteins of Rhodnius prolixus are named prolixins and consist of four related nitrophorin molecules [12,31], which are heme proteins that carry nitric oxide. The major component has a molecular weight of 19.69 kDa and inhibits factor VIII-mediated activation of factor X. Two proteins have been characterized from the saliva of Triatoma pallidipennis, triabin of 15.62 kDa, an inhibitor of thrombin based hydrolysis of fibrinogen [32], and pallidipin [33] of 19 kDa, an inhibitor of collagen-induced platelet aggregation. Functional studies of coagulation inhibition suggest that different species of Triatominae have functionally different mechanisms of coagulation inhibition and different SDS-PAGE profiles of salivary proteins [34]. These proteins, along with proteins having histamine binding, platelet inhibition, anticoagulation, and nitric oxide transport activities, are all members of the lipocalin family [35]. The three-dimensional structures of the nitrophorins NP1, 2, and 4 have been determined by x-ray crystallography. Many important vertebrate derived allergens are also members of the lipocalin family. An activatable serine protease of 40 kDa named triapsin, with an arginine specificity, has been isolated from the saliva of Triatoma infestans [36].
Investigation of anomalous charge variant profile reveals discrete pH-dependent conformations and conformation-dependent charge states within the CDR3 loop of a therapeutic mAb
Published in mAbs, 2020
Wenkui Lan, Joseph J. Valente, Andrew Ilott, Naresh Chennamsetty, Zhihua Liu, Joseph M. Rizzo, Aaron P. Yamniuk, Difei Qiu, Holly M. Shackman, Mark S. Bolgar
Conformational flexibility within the native state in particular in CDRs was described mainly using two models, the induced fit18 and conformational selection19 models. In principle, the induced fit model contends that a ligand is required to actively induce the protein into its binding-competent conformation while the conformational selection model contends that the binding-competent conformation preexists within the native state ensemble and that a ligand merely shifts the equilibrium toward that conformation. There are numerous examples in the literature that provide support for both models,20,21 but one particularly notable and recent report from Fernandez-Quintero et al.22 highlighted the importance of describing HC-CDR3 loop structures as conformational ensembles and concluded that all of the antibodies in their study demonstrated behavior consistent with the conformational selection model. Of the numerous extrinsic factors other than substrates that are known to influence such conformational changes, pH is among the most commonly cited. As pH can alter the ionization behavior of charged amino acid groups, changes in pH may interfere with favorable intramolecular interactions required for maintenance of certain folded structures. Under certain circumstances, it may even be possible to observe a pH-dependent equilibrium between two distinctly different native-state conformations, such as in the case of Nitrophorin-4 (NP4). Crystallographic data from Kondrashov et al.23 revealed that NP4 switches from a predominantly “closed” conformation at pH 5.6 to a predominantly “open” conformation at pH 7.4. Subsequent investigations by Menyhard et al.24 showed that an aspartic acid (Asp) that is buried in the closed conformation has an anomalously high pKa value, enabling it to remain protonated (uncharged) within the relatively nonpolar interior of the protein. Di Russo et al.25 then demonstrated the interconnectivity of pH-dependent conformational changes in NP4 and distinct conformation-dependent pKa values of the Asp in question. Specifically, these authors showed that in the open conformation, where the Asp side-chain is fully exposed to the solvent, its pKa was calculated as 4.3, consistent with theoretical values. In the closed conformation, however, intramolecular interactions with neighboring amino acids raised its calculated pKa to 8.5. Such coupling of pH-dependent conformational changes and conformationally dependent pKa values exemplifies the complex interdependencies that can contribute to the overall structure-function relationship of a protein.