Mammalian 20S Proteasome

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I. Introduction

A proteasome is a protein that is used in the cleavage of other proteins.  The degradation of a protein is important because it allows the cell to produce individual amino acids for new protein transcription, the removal of excess enzymes and the removal of transcription factors that are no longer needed.  The mammalian proteasome has a highly interesting 3-dimensional shape consisting of four heptameric rings stacked on each other.  Each ring contains seven smaller subunits or individual chains.  Each ring is presumed to be relatively similar to each other containing seven chains (subunits) that are the same.

For more information see Biochemistry Online: Chapter 7B - Mechanisms of Enzyme Catalysison

II. General Structure

Highlight Disulfide bridges
YDR Motif

The key highlighted amino acids are : Gly 8, Phe 9 and Asp 10.

Key amino acids are shown in yellow, with the gray showing the back bone structure of the protein. The YDR motif is an important part of 20S proteasome. Gly 8, Phe 9 and Asp 10 hold together the structural characteristics of the central core of the protein. They are shown above in yellow to highlight the fact their rigid nature in this protein helps to prevent the collapse of the central core and give this protein its characteristic shape.

Ext. Ring w/ Backbone
Interior Ring w/ Backbone
2nd Interior Ring w/ Backbone
2nd. Ext. Ring w/ Backbone
Single Ring w/ Individual Chains Highlighted

Each of the 4 major subunits break apart into 7 smaller chains that constitute the overall structure. This view shows each single chain of the subunit highlighted. Chain A is shown in the cartoon model, chain C in the spacefilling and Chain E in the wireframe. Each chain is highlighted with a different color for ease of distinguishing differences.