Camel (camelus dromedarius) milk PP3: evidence for an insertion in the amino-terminal sequence of the camel milk whey protein

The camel (camelus dromedarius) milk proteose peptone 3 (PP3) was purified successively by size exclusion fast protein liquid chromatography and rever sed phase high performance liquid chromatography and then characterized by amino acid residue composition determination and chemical microsequencing a fter CNBr or trypsin cleavages. In comparison with the previously reported structure of camel milk whey protein, the camel PP3 contains an insertion i n the N-terminal region which has approximately 24 residues, whereas the re maining C-terminal regions of these two homologous proteins are essentially identical. The camel PP3 seems to contain a potential O-glycosylation site localized in this insertion and 2 or 3 phosphorylated serine residues. PP3 belongs to the glycosylation-dependent cell adhesion molecule 1 (GlyCAM-1) family and could therefore play an immunological role in the camel or its suckling young.