Effects of a post-translational modification mutation on different developmentally regulated glycosidases in Dictyostelium discoideum

We have studied the effect of a post-translational modification mutation upon four developmentally regulated glycosidases of Dictyostelium discoideum. The presence of the modA mutation affects the intracellular level of these multimeric enzymes differently. The level of alpha-glucosidase is unaffected in the modA mutant. The mutant cell contains only a very small fraction of the wild type beta-glucosidase-1 activity. The alteration in modification renders beta-glucosidase-1 holoenzyme thermolabile and susceptible to degradation in vivo. alpha-Mannosidase-1 and N-acetylglucosaminidase are found at approximately 1/3 of the wild type level in the modA mutant. Degradation of holoenzyme does not appear to be responsible for the low level of these activities. We propose that alpha-mannosidase-1 and N-acetylglucosaminidase subunits are being degraded prior to subunit assembly. We conclude the modification bestows different properties upon the various glycosidases.