We have investigated the role of Asp60 of the alpha-subunit in allosteric communication between the tryptophan synthase alpha- and beta-subunits. Crystallographic and microspectrophotometric studies have been carried out on a mutant (alpha D60N) tryptophan synthase alpha 2 beta 2 complex which has no observable alpha-activity, but has substantial beta-activity. Single-crystal polarized absorption spectra indicate that the external aldimine is the predominant L-serine intermediate and that the amount of the intermediate formed is independent of pH, monovalent cations, and allosteric effectors. The three-dimensional structure is reported for this mutant enzyme complexed with indole 3-propanol phosphate bound to the alpha-site and L-serine bound to the beta-site (alpha D60N-IPP-Ser), and this structure is compared with that of the unliganded mutant enzyme (alpha D60N). In the complex, L-serine forms a stable external aldimine with the pyridoxal phosphate coenzyme at the active site of the beta-subunit. The conformation of the unliganded mutant is almost identical to that of the wild type enzyme. However, the structure of the mutant complexed with IPP and serine exhibits ligand-induced conformational changes much smaller than those observed previously for another mutant enzyme in the presence of the same ligands (beta K87T-IPP-Ser) [Rhee, S., Parris, K. D., Hyde, C. C., Ahmed, S. A., Miles, E. W., and Davies, D. R. (1997) Biochemistry 36, 7664-7680]. The alpha D60N-IPP-Ser alpha 2 beta 2 complex does not undergo the following ligand-induced conformational changes: (1) the closure of the alpha-subunit loop 6 (residues 178-191), (2) the movement of the mobile subdomain (residues 93-189) of the beta-subunit, and (3) the rotation of the alpha-subunit relative to the beta-subunit. These observations show that alpha Asp60 plays important roles in the closure of loop 6 and in allosteric communication between the alpha- and beta-subunits.
The line below this paragraph, {{ABSTRACT_PUBMED_9692955}}, adds the Publication Abstract to the page
(as it appears on PubMed at http://www.pubmed.gov), where 9692955 is the PubMed ID number.
-->
{{ABSTRACT_PUBMED_9692955}}
==About this Structure==
==About this Structure==
Line 31:
Line 35:
[[Category: L-serine in b-subunit]]
[[Category: L-serine in b-subunit]]
[[Category: Mutation d60n in a-subunit]]
[[Category: Mutation d60n in a-subunit]]
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 11:25:33 2008''
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jun 30 19:00:07 2008''
Revision as of 16:00, 30 June 2008
This article has been automatically seeded. Changes to this page should pertain to the PDB entry only and not to the protein or biomolecule in general.
