Smith David M, Kafri Galit, Cheng Yifan, Ng David, Walz Thomas, Goldberg Alfred L
Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA.
Mol Cell. 2005 Dec 9;20(5):687-98. doi: 10.1016/j.molcel.2005.10.019.
The archaeal ATPase complex PAN, the homolog of the eukaryotic 26S proteasome-regulatory ATPases, was shown to associate transiently with the 20S proteasome upon binding of ATP or ATPgammaS, but not ADP. By electron microscopy (EM), PAN appears as a two-ring structure, capping the 20S, and resembles two densities in the 19S complex. The N termini of the archaeal 20S alpha subunits were found to function as a gate that prevents entry of seven-residue peptides but allows entry of tetrapeptides. Upon association with the 20S particle, PAN stimulates gate opening. Although degradation of globular proteins requires ATP hydrolysis, the PAN-20S complex with ATPgammaS translocates and degrades unfolded and denatured proteins. Rabbit 26S proteasomes also degrade these unfolded proteins upon ATP binding, without hydrolysis. Thus, although unfolding requires energy from ATP hydrolysis, ATP binding alone supports ATPase-20S association, gate opening, and translocation of unfolded substrates into the proteasome, which can occur by facilitated diffusion through the ATPase.
古菌ATP酶复合物PAN是真核生物26S蛋白酶体调节性ATP酶的同源物，研究表明，在ATP或ATPγS结合时，而非ADP结合时，PAN会与20S蛋白酶体短暂结合。通过电子显微镜（EM）观察，PAN呈现为一种二环结构，覆盖在20S蛋白酶体上，类似于19S复合物中的两个密度区域。研究发现，古菌20S α亚基的N端起着门控的作用，可阻止七肽进入，但允许四肽进入。与20S颗粒结合后，PAN会刺激门控打开。虽然球状蛋白质的降解需要ATP水解，但含有ATPγS的PAN - 20S复合物可转运并降解未折叠和变性的蛋白质。兔源26S蛋白酶体在结合ATP时也能降解这些未折叠的蛋白质，而无需水解。因此，虽然蛋白质的展开需要ATP水解提供能量，但仅ATP结合就能支持ATP酶与20S的结合、门控打开以及未折叠底物转运到蛋白酶体中，这一过程可通过ATP酶介导的易化扩散实现。
