This project is concerned with the study of two enzymes involved in different steps of the lysosomal enzyme trafficking pathway. The first one, the cation independent mannose 6- phosphate receptor, transports lysosomal enzymes from the Golgi body to the endosome. Three domains of this protein provide binding sites for lysosomal enzymes, two of which have already been structurally characterised. Attempts to structurally elucidate the third domain are reported here. Production of a protein sample suitable for NMR studies was not achieved and further purification attempts were conducted on the human uncovering enzyme (UCE). This is the final protein in the pathway, which is responsible for the synthesis of the mannose 6-phosphate recognition tag on lysosomal enzymes. This also proved to be a difficult target and a UCE analogue from Streptococcus suis was produced instead, the structure of which was solved by NMR. NMR titration studies of the S. suis protein suggested that the substrate specificity of this enzyme was the same as that of the uncovering enzyme. To further investigate the possible function of this bacterial analogue, studies of single mutant knockouts of Streptococcus sanguinis were undertaken. A potential gene cluster containing the uncovering enzyme analogue was identified and knockout of one of these genes was found to lead to a deficiency in biofilm formation. This work did not give conclusive functions of these bacterial proteins, but it did open the door to further study of a bacterial system putatively described as being involved in prokaryotic protein glycosylation.