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Related Experiment Videos

Three-dimensional structure of beta-galactosidase from E. coli

R H Jacobson1, X J Zhang, R F DuBose

  • 1Institute of Molecular Biology, Howard Hughes Medical Institute, University of Oregon, Eugene 97403.

Nature
|June 30, 1994
PubMed
Summary

The structure of beta-galactosidase from Escherichia coli reveals a tetrameric enzyme with a 222-point symmetry. This atomic structure explains alpha-complementation and pushes the boundaries of protein crystallography.

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Molecular Biology

Background:

  • Beta-galactosidase (lacZ) from Escherichia coli is a key enzyme in molecular biology and was crucial for developing the operon model.
  • Understanding the enzyme's structure is vital for its applications and for deciphering biological mechanisms.

Purpose of the Study:

  • To determine the atomic structure of beta-galactosidase from Escherichia coli.
  • To elucidate the structural basis for alpha-complementation.

Main Methods:

  • X-ray crystallography was employed to determine the protein structure.
  • Non-crystallographic symmetry averaging was utilized as a powerful tool for structure determination.
  • Analysis of large protein crystals (unit cell dimensions >500 A, molecular mass ~2,000K per asymmetric unit) was performed.

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Main Results:

  • The structure reveals beta-galactosidase as a tetramer with 222-point symmetry.
  • Each polypeptide chain consists of 1,023 amino acids, folding into five sequential domains with an extended amino terminus.
  • The active site is formed by elements from two different subunits, and the amino-terminal segment participates in a subunit interface.

Conclusions:

  • The determined structure provides a structural explanation for the phenomenon of alpha-complementation.
  • This study demonstrates the feasibility of determining atomic structures for very large non-viral protein crystals.
  • The findings advance our understanding of enzyme structure-function relationships and protein crystallography techniques.