1A40

PHOSPHATE-BINDING PROTEIN WITH ALA 197 REPLACED WITH TRP

Summary for 1A40

• Entry DOI: 10.2210/pdb1a40/pdb
• Descriptor: PHOSPHATE-BINDING PERIPLASMIC PROTEIN PRECURSOR, PHOSPHATE ION (3 entities in total)
• Functional Keywords: phosphate-binding protein, mutagenesis, charge complementary, kinetics
• Biological source: Escherichia coli
• Total number of polymer chains: 1
• Total formula weight: 34667.70

Authors

Ledivina, P.S.,Wang, Z.,Tsai, A.,Koehl, E.,Quiocho, F.A. (deposition date: 1998-02-10, release date: 1999-03-23, Last modification date: 2024-05-22)

Primary citation

Ledvina, P.S.,Tsai, A.L.,Wang, Z.,Koehl, E.,Quiocho, F.A.
Dominant role of local dipolar interactions in phosphate binding to a receptor cleft with an electronegative charge surface: equilibrium, kinetic, and crystallographic studies.
Protein Sci., 7:2550-2559, 1998

PubMed Abstract: Stringent specificity and complementarity between the receptor, a periplasmic phosphate-binding protein (PBP) with a two-domain structure, and the completely buried and dehydrated phosphate are achieved by hydrogen bonding or dipolar interactions. We recently found that the surface charge potential of the cleft between the two domains that contains the anion binding site is intensely electronegative. This novel finding prompted the study reported here of the effect of ionic strength on the equilibrium and rapid kinetics of phosphate binding. To facilitate this study, Ala197, located on the edge of the cleft, was replaced by a Trp residue (A197W PBP) to generate a fluorescence reporter group. The A197W PBP-phosphate complex retains wild-type Kd and X-ray structure beyond the replacement residue. The Kd (0.18 microM) at no salt is increased by 20-fold at greater than 0.30 M NaCl. Stopped-flow fluorescence kinetic studies indicate a two-step binding process: (1) The phosphate (L) binds, at near diffusion-controlled rate, to the open cleft form (Po) of PBP to produce an intermediate, PoL. This rate decreases with increasing ionic strength. (2) The intermediate isomerizes to the closed-conformation form, PcL. The results indicate that the high specificity, affinity, and rate of phosphate binding are not influenced by the noncomplementary electronegative surface potential of the cleft. That binding depends almost entirely on local dipolar interactions with the receptor has important ramification in electrostatic interactions in protein structures and in ligand recognition.

PubMed: 9865949

Experimental method

X-RAY DIFFRACTION (1.7 Å)