Biochemical and functional properties of the full-length cation-dependent mannose 6-phosphate receptor expressed in Pichia pastoris

A glycosylation-deficient, full-length cation-dependent mannose 6-phosphate receptor (CD-MPR) containing a yeast signal sequence was expressed in Pichia pastoris using the constitutive promoter of the PGAP gene. The membrane-bound receptor was solubilized using detergents and purified by pentamannosyl phosphate-agarose affinity chromatography. Equilibrium binding studies identified a binding affinity of 2 nM for the lysosomal enzyme, beta-glucuronidase. To probe the linkage specificity of the recombinant CD-MPR, inhibition binding studies were conducted using non-phosphorylated oligomannoses which demonstrated that Manalpha1,2Man exhibits a 4-fold higher inhibition than Manalpha1,3Man and Manalpha1,6Man. The receptor was capable of associating into oligomeric forms and enzymatic deglycosylation revealed the presence of high-mannose sugars at the single potential N-glycosylation site. Mass spectrometric analysis revealed that the receptor was palmitoylated at the two potential cysteines in its cytoplasmic domain. In conclusion, the full-length CD-MPR produced in P. pastoris is structurally and functionally suitable for crystallization studies.