Taxonomic distribution of proteins containing CM_2 domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing CM_2 domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

Tyrosine and tryptophan act through the same binding site at the dimerinterface of yeast chorismate mutase.

Schnappauf G, Krappmann S, Braus GH
J Biol Chem. 1998; 273: 17012-7

Tyrosine and tryptophan are the regulators of the dimeric yeast chorismatemutase. Biochemical studies reveal two binding sites per molecule for botheffectors, tyrosine or tryptophan. A single binding site is built up byhelix 8 and helices 4 and 5 of two different subunits. The binding siteshave been analyzed in the active enzyme by site directed mutagenesis ofcritical codons of the coding gene, ARO7. Gly-141 and Ser-142, which bothreside on helix 8, are involved in the binding of tyrosine or tryptophanpresumably by interacting specifically with the amino- andcarboxylate-groups of these amino acid effectors. Interaction with Thr-145of helix 8 is required for a strong tyrosine binding to the allostericsite. Replacement of Arg-75, which connects helices 4 and 5 or of Arg-76,which is part of helix 5 by alanine residues, resulted in unregulatedenzymes. These two residues are bonded to the carboxylate group andphenolic hydroxyl group of tyrosine, respectively, but do not interactwith tryptophan by hydrogen bonding in the crystal structures.Phenylalanine, which has low binding affinity slightly activated thechorismate mutase. A T145V mutant chorismate mutase, however, showedincreased activation by phenylalanine. Our results support a mechanism bywhich tyrosine contracts the allosteric site by interacting with itsphenolic hydroxyl group. Tryptophan works in an inverse way by opening theallosteric site through the steric size of its side chain.

Chorismate mutase-prephenate dehydratase from Escherichia coli. Study ofcatalytic and regulatory domains using genetically engineered proteins.

Zhang S, Pohnert G, Kongsaeree P, Wilson DB, Clardy J, Ganem B
J Biol Chem. 1998; 273: 6248-53

The bifunctional P-protein, which plays a central role in Escherichia coliphenylalanine biosynthesis, contains two catalytic domains (chorismatemutase and prephenate dehydratase activities) as well as one R-domain (forfeedback inhibition by phenylalanine). Six genes coding for P-proteindomains or subdomains were constructed and successfully expressed.Proteins containing residues 1-285 and residues 1-300 retained full mutaseand dehydratase activity, but exhibited no feedback inhibition. Proteinscontaining residues 101-386 and residues 101-300 retained full dehydrataseactivity, but lacked mutase activity. Fluorescence emission spectra andbinding assays indicated that residues 286-386 were crucial forphenylalanine binding. The mutase (residues 1-109), dehydratase (residues101-285), and regulatory (residues 286-386) activities were thus shown toreside in discrete domains of the P-protein. Both the mutase domain andthe native P-protein formed dimers. Deletion of the mutase domaindiminished phenylalanine binding to the regulatory site as well asprephenate binding to the dehydratase domain, both through cooperativeeffects. Besides eliminating feedback inhibition, removal of the R-domaindecreased the affinity of chorismate mutase for chorismate.