NDLI: Origin of the mutual activation of the alpha and beta 2 subunits in the alpha 2 beta 2 complex of tryptophan synthase. Effect of alanine or glycine substitutions at proline residues in the alpha subunit.

Content Provider	Journal of Biological Chemistry (JBC)
Author	Ogasahara, K. Hiraga, K. Ito, W. Miles, E. W. Yutani, K.
Abstract	To understand how the alpha and beta 2 subunits of tryptophan synthase from Escherichia coli interact to form an alpha 2 beta 2 complex and undergo mutual activation, we have investigated alpha subunits with single amino acid replacements at conserved proline residues. Although the activities of alpha 2 beta 2 complexes that contain wild type alpha subunit or alpha subunits substituted at positions 28, 62, 96, and 207 are similar, the activities of alpha 2 beta 2 complexes that contain alpha subunits substituted at positions 57 and 132 are remarkably altered. Whereas the latter enzymes have greatly reduced activities in the individual half-reactions, they have considerably higher activities in the overall reaction. These remarkable activity results are explained by a decrease in the affinity of these mutant alpha subunits for the beta 2 subunit and by an increase in the affinity in the combined presence of ligands of both the alpha subunit and the beta 2 subunit. Isothermal calorimetric titrations of wild type beta 2 subunit with wild type alpha subunit and a mutant alpha subunit containing a substitution of glycine for proline at position 132 show that both the affinity and the exothermic association enthalpy are greatly reduced in the mutant alpha subunit although the stoichiometry of association is unchanged. The affinity of the mutant alpha subunit for the beta 2 subunits is greatly increased in the presence of an alpha subunit ligand, alpha-glycerol phosphate. We conclude that proline 132 plays a critical role in subunit interaction and in mutual subunit activation.
Related Links	http://www.jbc.org/content/267/8/5222.abstract
Ending Page	5228
Starting Page	5222
Page Count	7
File Format	HTM / HTML PDF
ISSN	00219258
Journal	Journal of Biological Chemistry (JBC)
Issue Number	8
Volume Number	267
e-ISSN	1083351X
Language	English
Publisher	American Society for Biochemistry and Molecular Biology
Publisher Date	1992-03-15
Access Restriction	Open
Content Type	Text
Resource Type	Article
Subject	Cell Biology Biochemistry Molecular Biology

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Threonine 183 and adjacent flexible loop residues in the tryptophan synthase alpha subunit have critical roles in modulating the enzymatic activities of the beta subunit in the alpha 2 beta 2 complex.

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A novel intersubunit repair mechanism in the tryptophan synthase alpha 2 beta 2 complex. Critical role of the beta subunit lysine 167 in intersubunit communication.

Effect of amino acid residues on conformational stability in eight mutant proteins variously substituted at a unique position of the tryptophan synthase alpha-subunit.

Three-dimensional structure of the tryptophan synthase alpha 2 beta 2 multienzyme complex from Salmonella typhimurium.

Site-specific mutagenesis of the alpha subunit of tryptophan synthase from Salmonella typhimurium. Changing arginine 179 to leucine alters the reciprocal transmission of substrate-induced conformational changes between the alpha and beta 2 subunits.

Mutagenesis of the amino-terminal glycine to alanine in Gs alpha subunit alters beta gamma-dependent properties and decreases adenylylcyclase activation.

Location of three active site residues in the NH2-terminal sequence of the beta 2 subunit tryptophan synthase from Escherichia coli.

Origin of the mutual activation of the alpha and beta 2 subunits in the alpha 2 beta 2 complex of tryptophan synthase. Effect of alanine or glycine substitutions at proline residues in the alpha subunit.

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Threonine 183 and adjacent flexible loop residues in the tryptophan synthase alpha subunit have critical roles in modulating the enzymatic activities of the beta subunit in the alpha 2 beta 2 complex.

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Effect of amino acid residues on conformational stability in eight mutant proteins variously substituted at a unique position of the tryptophan synthase alpha-subunit.

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