Pam16

Pam16 is a mitochondrial inner-membrane protein that is a component of the PAM (presequence translocase-associated motor) complex, which powers the translocation of proteins across the inner mitochondrial membrane through the TIM23 complex. Pam16 functions together with Pam18, a J-domain protein, to regulate the activity of the mitochondrial Hsp70 chaperone (mtHsp70; Ssc1 in yeast), driving ATP-dependent pulling of precursor proteins into the matrix.

Unlike classical J-domain proteins, Pam16 contains a J-domain-like region but lacks the conserved HPD motif; accordingly, it acts as a regulatory subunit rather than a typical J-protein. In Saccharomyces cerevisiae, Pam16 forms a heterodimer with Pam18 and, together with Tim44, constitutes the motor that couples ATP hydrolysis by mtHsp70 to precursor translocation. The PAM core is important for efficient import and mitochondrial biogenesis; loss or impairment of Pam16 disrupts import and can cause growth defects.

In mammals, the functional counterpart is MAGMAS, a Pam16 homolog that interacts with a J-domain protein ortholog (DNAJC19) to form the mammalian TIM23 import motor. The MAGMAS–DNAJC19 complex is anchored in the inner membrane and contributes to regulating mtHsp70 during precursor translocation.

Overall, Pam16 is a conserved regulator of mitochondrial protein import, linking the TIM23 translocon to the mtHsp70 motor through a J-domain–like regulatory module.