Human Pex19p Binds Peroxisomal Integral Membrane Proteins at Regions Distinct from Their Sorting Sequences

Abstract

The molecular machinery underlying peroxisomal membrane biogenesis is not well understood. The observation that cells deficient in the peroxins Pex3p, Pex16p, and Pex19p lack peroxisomal membrane structures suggests that these molecules are involved in the initial stages of peroxisomal membrane formation. Pex19p, a predominantly cytosolic protein that can be farnesylated, binds multiple peroxisomal integral membrane proteins, and it has been suggested that it functions as a soluble receptor for the targeting of peroxisomal membrane proteins (PMPs) to the peroxisome. An alternative view proposes that Pex19p functions as a chaperone at the peroxisomal membrane. Here, we show that the peroxisomal sorting determinants and the Pex19p-binding domains of a number of PMPs are distinct entities. In addition, we extend the list of peroxins with which human Pex19p interacts to include the PMP Pex16p and show that Pex19p's CaaX prenylation motif is an important determinant in the affinity of Pex19p for Pex10p, Pex11p␤, Pex12p, and Pex13p.

Peroxisomal Membrane Proteins Contain Common Pex19p-binding Sites that Are an Integral Part of Their Targeting Signals

“…This result also demonstrated the occurrence of multiple binding sites in at least some PMPs as reported previously for mammalian Pmp34p and Pmp22p (Jones et al, 2001;Brosius et al, 2002). The only Pex19p-binding site in higher eukaryotes that has been characterized in detail so far is that of Homo sapiens Pex13p (Fransen et al, 2001). Aligning the Pex13p protein sequences from several species revealed that the Pex19p-binding site of S. cerevisiae represents a highly conserved region within the protein.…”

“…Pex19p interacts with multiple PMPs (Gö tte et al, 1998;Sacksteder et al, 2000;Snyder et al, 2000;Fransen et al, 2001); however, precise Pex19p-binding sites have not yet been dissected and the physiological role of these interactions is under debate. We show here for the first time that Pex19p-binding sites represent short sequences that share a common motif and are integral parts of mPTSs and that these sites are required for the targeting of PMPs.…”

“…Although some similarities among these basic sequences have been noted, a clear consensus could not yet be deduced. Noteworthy, some PMPs have been shown to contain multiple nonoverlapping mPTS (Fransen et al, 2001;Jones et al, 2001;Brosius et al, 2002).…”

“…Among the three peroxins with a potential role in PMP targeting identified to date, only Pex19p possesses some features of an mPTS recognition factor, as it is largely cytosolic (Gö tte et al, 1998) and interacts with a number of PMPs in all species tested Fransen et al, 2001). Evidence is accumulating that Pex19p is indeed able to bind mPTS (Brosius et al, 2002;Jones et al, 2004), albeit other reports claimed that Pex19p binds some PMPs at regions that appear to be different from their sorting sequences Fransen et al, 2001Fransen et al, , 2004. All these reports examined rather large PMP fragments for Pex19p binding and failed to detect any similarities between the different Pex19p-interacting fragments.…”

“…Although some similarities among these basic sequences have been noted, a clear consensus could not yet be deduced. Noteworthy, some PMPs have been shown to contain multiple nonoverlapping mPTS (Fransen et al, 2001;Jones et al, 2001;Brosius et al, 2002).Targeting-specific elements of an mPTS are expected to be recognized by a specific import receptor (signal recognition factor). Among the three peroxins with a potential role in PMP targeting identified to date, only Pex19p possesses some features of an mPTS recognition factor, as it is largely cytosolic (Gö tte et al, 1998) and interacts with a number of PMPs in all species tested Fransen et al, 2001 Pex19p is indeed able to bind mPTS (Brosius et al, 2002;Jones et al, 2004), albeit other reports claimed that Pex19p binds some PMPs at regions that appear to be different from their sorting sequences Fransen et al, 2001Fransen et al, , 2004.…”