Characterisation of the normal canine serum proteome using a novel electrophoretic technique combined with mass spectrometry

One dimensional (1D) serum protein electrophoresis (SPE) on agarose gels is a frequently used diagnostic tool for canine diseases; however, little is known regarding the precise composition of the different protein fractions in normal or diseased animals. In this study, to analyse the canine serum proteome in more detail, conventional 1D SPE was combined with second dimension (2D) polyacrylamide gel electrophoresis (PAGE), followed by tandem mass spectrometry (MS). One dimensional SPE was performed on the sera of 17 healthy dogs to establish normal reference ranges for the albumin and globulin sub-fractions. Two representative serum samples from healthy dogs were further separated using a novel method of 2D PAGE, leading to the generation of 26 distinct bands across the six main sub-fractions, which were subjected to MS analysis. Thirty-two proteins were identified, most of which were found in both dogs. Twenty proteins belonged specifically to the species Canis lupus familiaris, with the remaining 12 proteins belonging to other mammalian species, likely reflecting incomplete sequencing knowledge of canine proteins. Two dimensional electrophoresis and MS allowed identification of canine serum albumin precursor, serpin peptidase inhibitor, kininogen-1, vitamin D binding protein, haemopexin, complement C4 and a variety of immunoglobulin class molecules, along with localisation of these proteins within serum protein subfractions.