View source for 1a40

[[Image:1a40.gif|left|200px]]<br /><applet load="1a40" size="350" color="white" frame="true" align="right" spinBox="true" 
caption="1a40, resolution 1.70&Aring;" />
'''PHOSPHATE-BINDING PROTEIN WITH ALA 197 REPLACED WITH TRP'''<br />

==Overview==
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.

==About this Structure==
1A40 is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli] with <scene name='pdbligand=PO4:'>PO4</scene> as [http://en.wikipedia.org/wiki/ligand ligand]. Known structural/functional Site: <scene name='pdbsite=BNG:The+Site+Binds+Phosphate+Specifically'>BNG</scene>. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1A40 OCA]. 

==Reference==
Dominant role of local dipolar interactions in phosphate binding to a receptor cleft with an electronegative charge surface: equilibrium, kinetic, and crystallographic studies., Ledvina PS, Tsai AL, Wang Z, Koehl E, Quiocho FA, Protein Sci. 1998 Dec;7(12):2550-9. PMID:[http://ispc.weizmann.ac.il//pmbin/getpm?pmid=9865949 9865949]
[[Category: Escherichia coli]]
[[Category: Single protein]]
[[Category: Koehl, E.]]
[[Category: Ledivina, P.S.]]
[[Category: Quiocho, F.A.]]
[[Category: Tsai, A.]]
[[Category: Wang, Z.]]
[[Category: PO4]]
[[Category: charge complementary]]
[[Category: kinetics]]
[[Category: mutagenesis]]
[[Category: phosphate-binding protein]]

''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun Feb  3 09:28:55 2008''