Identification of the native N-terminus of the membrane attaching ferriheme protein nitrophorin 7 from Rhodnius prolixus.

All species of the genus Rhodnius have a characteristic red coloration in their salivary glands due to the presence of heme proteins. Some of these secreted proteins, known as nitrophorins (NPs), are responsible for many of the antihemostatic activities of Rhodnius saliva such as anticoagulant and antihistamine. Several NPs have been described (NP1-4 and NP7), where NP7 is the only one with affinity to phospholipid membranes. Computational prediction suggested that NP7 also has an extended N-terminal tail on signal peptide cleavage; however, the complementary DNA does not allow the determination of the exact site of signal peptidase cleavage. On the other hand, according to previous studies, the exact length of the N-terminus has important consequences for the nitric oxide binding properties of NP7. Here, a method was developed to select phospholipid membrane-attaching proteins from homogenized tissue for analysis by mass spectrometry. The method was used to determine the exact N-terminus of the ferriheme protein NP7 from homogenates of the salivary glands of 5th instar nymphal stages of Rhodnius prolixus.