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Preliminary Results on the Crystal and Molecular Structure of Native and Mutant Aspartate Carbamoyltransferase at Neutral pH
Author(s) -
Lu TianHuey,
Young TiSheng,
Schachman Howard,
Kim SungHou
Publication year - 1988
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.198800047
Subject(s) - aspartate carbamoyltransferase , chemistry , random hexamer , mutant , protein subunit , amino acid , biochemistry , stereochemistry , transferase , enzyme , allosteric regulation , gene
Abstract The cell dimensions are a=b=131.2, c=198.5 Å, and α= β =90°, γ = 120° for both the wild and the mutant types of aspartate transcarbamoylase (ATCase) crystallized at pH=7.0. The space group is R32. Although the mutant and wild forms of ATCase show large differences in enzyme activity and chemical reactivity, yet they are isomorphous in structure. One asymmetric unit of ATCase contains a catalytic subunit, molecular weight 34,000 daltons, and a regulatory subunit, molecular weight 17,000. There are 310 amino acids in the catalytic subunit and 162 amino acids plus zinc in the regulatory subunit. The whole ATCase is a hexamer and consists of six molecules of catalytic and regulatory subunits. The primary structure study of this enzyme shows that the mutant form has a single substitution of aspartic acid in place of glycine at position 128 in the amino acid sequence of the catalytic chains. In most part of the sequence, the regulatory and catalytic chains of mutant and wild forms of ATCase are in similar conformations. (2Fo‐Fc) syntheses displayed with computer graphics using the FRODO program, were applied to the reflection data from both mutant and wild types. A stereoview of certain regions displayed on PS300 graphics shows significant differences between the wild and mutant types of ATCase.