Intracellular proteins, including short-lived proteins such as cyclin, Mos, Myc, p53, NF-kappaB, and IkappaB, are degraded by the ubiquitin-proteasome system. The 26S proteasome is a self-compartmentalising protease responsible for the regulated degradation of intracellular proteins in eukaryotes [, ]. This giant intracellular protease is formed by several subunits arranged into two 19S polar caps, where protein recognition and ATP-dependent unfolding occur, flanking a 20S central barrel-shaped structure with an inner proteolytic chamber. This overall structure is highly conserved among eukaryotes and is essential for cell viability. Proteins targeted to the 26S proteasome are conjugated with a polyubiquitin chain by an enzymatic cascade before delivery to the 26S proteasome for degradation into oligopeptides.The 26S proteasome can be divided into two subcomplexes: the 19S regulatory particle (RP) and the 20S core particle (CP) []. The 19S component is divided into a "base"subunit containing six ATPases (Rpt proteins) and two non-ATPases (Rpn1, Rpn2), and a "lid"subunit composed of eight stoichiometric proteins (Rpn3, Rpn5, Rpn6, Rpn7, Rpn8, Rpn9, Rpn11, Rpn12) []. Additional non-essential and species specific proteins may also be present. The 19S unit performs several essential functions including binding the specific protein substrates, unfolding them, cleaving the attached ubiquitin chains, opening the 20S subunit, and driving the unfolded polypeptide into the proteolytic chamber for degradation. The 26s proteasome and 19S regulator are of medical interest due to their involvement in burn rehabilitation [].This group represents a 26S proteasome regulatory complex, non-ATPase subcomplex, Rpn1 (regulatory-particle non-ATPase subunit 1). This subunit is essential for embryogenesis in Arabidopsis thaliana [].
The 26S proteasome is the major ATP-dependent protease in eukaryotes which plays a key role in intracellular protein degradation [, ].This domain is found at the N terminus of the 26S proteasome regulatory subunit RPN1 (also known as 26S proteasome non-ATPase regulatory subunit 2 (PSMD2)) []. The domain is formed by an array of alpha helices [].
This is the C-terminal domain found in RPN1 proteins (26S proteasome non-ATPase regulatory subunit 2). The 26S proteasome holocomplex consists of a 28-subunit barrel-shaped core particle (CP) in the centre capped at the top and bottom by 19-subunit regulatory particles (RPs). The CP forms the catalytic chamber and the RP is formed from two subcomplexes known as the lid and the base []. The lid comprises nine Rpn subunits in yeast (Rpn3/5/6/7/8/9/11/12/15) and the base comprises three Rpn subunits (Rpn1/2/13) and six ATPases (Rpt1-6) [].
