Proteasome immunoproteasome

Human ySli, pli and y 5i subunits are 59.2%, 57.7% and 68.6% identical, respectively, with their constitutively active cotmterparts pi, pi and 5, and 46.0%, 46.0% and 57.6% identical, respectively with the pi, pi and ps subunits in yeast. Indeed, all induced subunits of the human 20S proteasome have higher sequence similarity to the corresponding subunits of the human constitutive proteasome than to their yeast counterparts. Both of the human proteasomes share the remaining four p subunits and all the a subunits. Therefore, the X-ray structure of the bovine 20S proteasome was used for more accurate prediction of the three-dimensional structure of the immunoproteasome (Fig. 3.6). 

Fig. 3.6 Structure comparison of the active centers of the constitutive proteasome with the active centers of the immunoproteasome. (a), (b) Diagrams of eiectrostatic surface po-tentiai of SI pockets for the and i active sites. Red and biue indicate negative and positive potentiais, respectiveiy. The SI pocket is surrounded by a dotted circie. The SI pocket of the p active center is formed by both and fn subunits, (a) The SI pocket of the ySl active center is charged positiveiy at the pi subunit side and negativeiy at the p subunit...

Tanaka, K., Kasahara, M., The MHC class 1 ligand-generating system roles of immunoproteasomes and the interferon-gamma-indudble proteasome activator PA28. Immunol. Rev. 1998, 363, 161-176. 

S complexes can form which function in specific degradation reactions. In the pro-teasome that is involved in processing antigenic peptides the catalytic reactions are performed by E-subunits different from the the X,Y and Z subunits. This specific proteasome is also called immunoproteasome . 

Immunoproteasome Constitutive proteasome Figure 12.1 Evolution of proteasome 20S core particles. 

Treatment of either a tissue culture or a cell extract with Bodipy-epoxomicrn MVB-003 followed by SDS-PAGE readily reveals proteasome active sites (Figure 12.3c) [9, 10]. In case the constitutive proteasome is expressed exclusively, the three catalytic species pi, P2, and pS are readUy resolved. In case the treated tissue also expresses immunoproteasomes, the one-dimensional gel wUl resolve pi and p2i, but only partially pi, pii, pS, and pSi (see for a detailed experimental protocol Box 12.1 [11]). Two-dimensional gel electrophoresis, by which proteins are separated on the basis of the charge followed by mass allows for complete resolution of all six catalytic activities. Figure 12.3d represents an example of competitive ABPP. In this experiment, tissue or tissue extract is treated first with a prospective inhibitor. Ensuing incubation with... 

Ferrer I, MartinB, Castano JG et al. (2004) Proteasomal expression, induction of immunoproteasome suhunits, and local MHC class I presentation in myofibrillar myopathy and inclusion body myositis. J Neuropathol Exp Neurol 63, 484-498. 

---