Developmental regulation of Dictyostelium discoideum plasma membrane proteins.

Abstract

Developmental changes in the plasma membrane proteins of D. discoideum were studied using metabolic labeling with [35S]methionine and 2-dimensional electrophoresis. Pulse labeling for 1 h at the early interphase, late interphase, aggregation and tip formation stages of development showed that the profile of newly synthesized plasma membrane proteins changed dramatically over this interval. Only 14% of the polypeptide species were synthesized at all 4 stages at detectable levels; 86% of the species changed over this developmental interval according to the criterion that they were synthesized at some but not all of the 4 stages tested. Long-term labeling during vegetative growth followed by initiation of development showed that the steady-state levels of the plasma membrane proteins changed very little over the same period. The only changes were in minor species (33% overall change). Similar analyses of whole cell proteins showed 27 and 20% change, respectively. Cell surface radioiodination revealed 52 external proteins in the plasma membrane. Comparison with the uniform methionine labeling results showed that these proteins were, with 1 notable exception, minor membrane components. In these external proteins developmental changes were limited and were observed in the less abundant species. These results demonstrate the existence of 2 general classes of plasma membrane proteins. The first is a population of high-abundance proteins that are present in vegetative cells and are largely conserved through development. These possibly serve housekeeping functions common to all stages. The 2nd class consists of low-abundance species that are expressed in a highly stage-specific manner and which presumably participate in developmentally important functions.