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I. Introduction

This protein contains both alpha helices and beta sheets. There are two main classes of these proteins. One is the beta-barrel of TIM. This class consists of open twisted beta-sheets structure with helices on both sides of the sheet. These structures can differ greatly (in the number of beta strands (4-10) and in the fact that beta strands continuous in the primary structure may not be adjacent in the beta sheet). The active site is a crevice comprised of the region around the carboxy-terminus of the parallel beta strands. 

For more information see Biochemistry Online: Chapter 2C - Understanding Protein Conformation

II. General Structure

Backbone and sidechains
Cartoon, Hbonds and Wireframe
Dot surface and Wireframe