Eral1 is a GTPase and ribosomal assembly factor of the mitochondrial small subunit (SSU). Eral1 binds 12SrRNA at a critical juncture, and its association and dissociation are necessary for mitoribosome maturation. Previous work in the literature indicated the proteolytic complex mitochondrial ClpXP (mtClpXP) as a regulator of dissociation: mtClpXP physically associates with Eral1 in vivo and knockout of ClpP results in Eral1 stabilization, accumulation of Eral1-bound small subunit precursors, and reduced levels of mature mitoribosomes. In order for mtClpXP to both permit Eral1 association and enact its dissociation from the assembling small subunit, it must either recognize a specific Eral1 conformation that indicates completion of its assembly factor function or precisely tune Eral1 levels to achieve a metastable state. We aim to describe the recognition strategy that mtClpXP utilizes to unfold and degrade Eral1 and enable ribosome assembly. We have demonstrated that mtClpXP directly unfolds and degrades Eral1 in vitro. Evolutionary coupling analysis between human Eral1 and mtClpX has pointed to select residues that may mediate the interaction between these proteins. We have shown that mutation of at least one such Eral1 residue blocks its unfolding and degradation. We are utilizing a peptide SPOT array to characterize additional Eral1 motifs that assist in recognition and unfolding by mtClpX and hypothesize that the exposure of these sequences aligns with the Eral1 state that is recognized by mtClpX.
