Unfolded protein exhibits antiassociation activity toward the 50S subunit facilitating 70S ribosome dissociation

The ability of the ribosome to assist in the folding of proteins both in vitro and in vivo is well documented. The interaction of an unfolded protein with the peptidyltransferase center of the bacterial large ribosomal subunit is followed by release of the protein in a folding-competent state and rapid dissociation of ribosome into its subunits. Our studies demonstrate that the 50S subunit-associated antiassociation ability of an unfolded protein might contribute significantly to its ability to mediate energy-independent and stable dissociation of the ribosome into its subunits. The stoichiometry of the protein present with respect to the ribosome is an important factor in determining whether the ribosome has a chaperoning effect on protein folding or if the protein acts as a 50S subunit antiassociation factor. Sustained interaction of the protein with the ribosome at higher protein concentrations and the hindrance in the formation of the central intersubunit bridge B2a could underlie the antiassociation activity of unfolded proteins. The ribosome dissociation and antiassociation activity of unfolded proteins could make the ribosome susceptible to cellular ribonucleases, thereby initiating ribosome degradation, which is a well-documented phenomenon under nutrient deprivation conditions.