ABOUT

Our group studies the molecular mechanisms of peroxisomal biogenesis, a process affected in several human genetic disorders. Our main focus is on a group of proteins which comprise the peroxisomal matrix protein Import machinery (PIM). These proteins include the RING finger peroxins (PEX2, PEX10 and PEX12) and other components of the ubiquitin-conjugating cascade (e.g., E2D1/2/3), ATPases of the AAA family (PEX1 and PEX6) as well as a group of proteins that comprise the peroxisomal protein translocon (e.g., PEX13 and PEX14). Thus, the general goal is not only to understand how newly synthesized (cytosolic) peroxisomal proteins are recognized, and translocated across the peroxisomal membrane in an already folded conformation, but also to contribute to a better understanding of the mechanisms used by AAA ATPases to remodel protein complexes and how protein activity can be modulated by transient ubiquitination. More recently, we are also interested in understanding the mechanisms of redox homeostasis in peroxisomes. We mainly use biochemical approaches to address these topics and we have developed a powerful cell-free in vitro system that recapitulates all the steps of peroxisomal protein import pathway.

RESEARCH

In the last years, our group has made several important findings. One regards the conclusion that PEX5, the shuttle receptor for newly synthesized peroxisomal matrix proteins, is also a chaperone/holdase that binds its cargoes in the cytosol inhibiting their oligomerization. This finding, together with the observation that the monomeric versions of some peroxisomal proteins are far better substrates for the PIM than the corresponding oligomeric versions, argues against the long-proposed concept that peroxisomal proteins are imported into the organelle matrix already in their oligomeric native state.

In another study, the nature of the peroxisomal protein translocon was addressed. In contrast to current models claiming that PEX5 is a pore-forming toxin-like protein that becomes inserted into the peroxisomal membrane during the protein transport process, we found evidence suggesting that the peroxisomal protein translocon is actually the so-called docking/translocation module (a complex comprising PEX2, PEX10, PEX12, PEX13 and PEX14) which forms a large hydrophilic cavity into which PEX5 enters to release its cargoes.

Finally, new mechanistic data on PEX1 and PEX6 were also obtained. We demonstrated that DTM-embedded monoubiquitinated PEX5 is the bona fide substrate for these AAA ATPases and that PEX5 is globably unfolded during the ATP-dependent dislocation event, re-enforcing the idea that these mechanoenzymes unfold substrates using a processive threading mechanism.