Using mass spectrometry to detect buffalo salivary odorant-binding protein and its post-translational modifications

A large number of mammalian odorant-binding proteins, which are lipocalins, have been studied. These proteins participate in peri-receptor events by selecting and carrying odorant molecules. The present study aimed at identifying the buffalo salivary odorant-binding protein (sOBP), and to determine its post-translational modification using mass spectrometry. The buffalo salivary 21kDa protein was initially separated adopting sodium dodecyl sulfate-polyacrylamide gel electrophoresis and it was identified as sOBP with high statistical reliability using liquid chromatography/tandem mass spectrometry (LC/MS/MS) and SEQUEST, for the first time. Further, the post-translationally modified peptides were screened adopting MS/MS. A total of four post-translational modifications, namely glycation at lysine-⁵⁹, hydroxylation at lysine-¹³⁴, ubiquitination at lysine- ¹²¹, and dihydroxylation in lysine-¹⁰⁸, were recorded. Moreover, these modifications have not been identified in buffalo salivary odorant-binding protein.