Survey of the camel urinary proteome by shotgun proteomics using a multiple database search strategy

We report the first survey of the dromedary camel urinary proteome. Proteins retained from ultrafiltration of urine were analysed by GeLC-MS/MS (SDS-PAGE followed by LC-MS/MS). In the absence of a complete camel genome sequence, the number of protein identifications was maximised by searching three primary sequence databases: Swiss-Prot, alpaca and camel EST. This search strategy enabled the identification of 1274 peptide sequences, of which 735 were found in at least two independent samples. Functional annotations for proteins identified from alpaca and camel EST sequences were mapped from basic local alignment search tool (protein) searches. These 735 peptides, which included many novel sequences found only in the camel EST database, were grouped to 147 protein descriptors. Gene ontology term analysis of human proteins with sequence similarity showed that camel urine may be particularly enriched in proteins from extracellular compartments and vesicles, and with functions that include carbohydrate-binding and peptidase inhibitor activities. If their biological functions are conserved between species, many of the camel urinary proteins could be involved in various stress and immune responses, and some may have antimicrobial activities.