Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology
ReviewNitrophorins and related antihemostatic lipocalins from Rhodnius prolixus and other blood-sucking arthropods
Section snippets
Blood feeding and the spread of Chagas’ disease
Rhodnius prolixus, a small insect prevalent in South America but also found in North America, feeds on the blood of rodents and larger mammals, including humans. The insect is a relatively slow feeder, and probes the tissue until a suitable internal wound is created, or a blood vessel is tapped [1]. Like most blood-sucking insects, Rhodnius secretes a protein-rich saliva to aid in the taking of a blood meal. Nine salivary proteins have been characterized from Rhodnius, and all nine have
Nitrophorin structure
The initial isolation and characterization of the nitrophorins was accomplished by the fractionation of hundreds of pairs of Rhodnius salivary glands obtained through painstaking insect dissections. All four nitrophorins were identified from this source, and all three antihemostatic activities (NO transport, histamine binding, and anticoagulation) were discovered [11], [12], [13], [14], [20], [21], [22]. The subsequent cloning and expression of all four nitrophorins led to more detailed
Nitrophorin delivery of nitric oxide
Nitric oxide has long been of interest to chemists for its use as a spectroscopic probe, for the wide range of coordination chemistry it allows, and for its usefulness in molecular orbital theory (recently reviewed in [34]). More recently, biologists have found NO to be a signaling molecule in virtually all vertebrate cells and possibly all eukaryotic cells. The choice by nature of NO as a signaling molecule is curious since it is extremely reactive, due to an unpaired, antibonding electron,
Histamine binding by salivary proteins from R. prolixus and tick
Slow feeding blood-sucking insects such as ticks and R. prolixus face a difficulty: the tissue damage they cause results in inflammation and their salivary proteins illicit an immune response, which can lead to the ‘walling off’ of the affected area, or to the detection and execution of the insect. To overcome this problem these insects sequester histamine, the signaling molecule secreted by the host’s mast cells in response to tissue trauma. R. appendiculatus [5] and R. prolixus [22], [27]
Anticoagulation by NP2 and triabin
While feeding, blood-sucking insects must prevent blood coagulation so that blood will flow from the wound and not clog the insect’s mouth parts and gut. The saliva of R. prolixus has long been known to act as an anticoagulant [13]. Interestingly, this activity resides in NP2, also called prolixin-S, and thus provides a third activity in the nitrophorin lipocalin fold [12], [14]. Like all of the Rhodnius antihemostatic activities, NP2 acts early in the blood coagulation cascade. Exposure of
Antiplatelet activity in R. prolixus, T. pallidipennis, and Ornithodoros moubata
At the site of an injury, platelets are activated and adhere to exposed collagen in the blood vessel wall [44]. Binding directly activates platelets by a receptor-mediated signal transduction pathway, inducing pronounced alterations in platelet shape and biochemistry. Activated platelets secrete factors such as thromboxane A2 and ADP that promote further platelet aggregation, and provide the phospholipid surface necessary for the blood-coagulation cascade. The extent of platelet aggregation is
Evolution and pharmacology
Thus, a curious story is unfolding concerning the means by which insects have gained the ability to feed on blood. This ability has independently evolved in several species, and generally the same steps in hemostasis are targeted by proteins in the insects’ saliva [3]. The lipocalin fold appears to be a protein scaffold of choice for the development of antihemostatic functions in insects, based on the prevalence of this fold in multiple blood-feeding organisms, and 13 such proteins are known (
Acknowledgements
We thank Dr. Guido Paesen for sending us the HBP2 coordinates prior to release from the protein data bank. This work was supported in part by NIH grants HL62969 and GM58727, and ADCRC grant 1-208A.
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