ISSN:
0091-7419
Keywords:
L-arabinose-binding protein
;
three-dimensional structure
;
spectrochemical studies
;
active transport
;
chemotaxis
;
Life Sciences
;
Molecular Cell Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
The crystal structure of the L-arabinose-binding protein (ABP), an essential component of the high affinity L-arabinose transport system in E. coli, has been determined at 3.5- and 2.8-Å resolutions. The Fourier maps indicate that the molecule is ellipsoidal with overall dimensions of 70 × 35 × 35 Å (axial ratio ≃ 2:1) and consists of 2 distinct globular domains (designated “P” and “Q”). A tentative trace of the polypeptide backbone is presented. The 2 domains are arranged to create a deep and narrow cleft, the base of which is which is formed by 3 polypeptide chain segments linking the 2 domains. The arrangements of the secondary structure of the 2 domains are remarkably similar and can be related by a pseudo-twofold axis. Each domain has a pleated sheet core with 2 helices on either side of the plane of the β sheet. This secondary structural arrangement is similar to that found in other proteins, specifically the dehydrogenases and kinases. The structural similarity is particularly intriguing in light of the recent finding in this laboratory that the dye 2′,4′,5′,7′-tetraiodofluorescein, an adenine analogue which has been shown to bind to several dehydrogenases and kinases, binds to ABP with a dissociation constant of 30 μM.Experiments performed with protein, modified with the chromophoric probe 2-chloromercuri-4-nitrophenol (MNP), suggest that the binding site is near an essential cysteine residue: modification of the thiol with the mercurial dramatically decreases the ligand-binding affinity of ABP, and conversely, the sugar protects the cysteine from reaction with MNP. The binding of L-arabinose to MNP-labeled protein perturbs the nitrophenol absorbance spectrum. The essential cysteine has been assigned to position 64 in the proposed chain tracing, which is consistent with the amino acid sequence. As an explanation for the failure of the difference Fourier analyses to locate the sugar-binding site, it is postulated that the structure has been solved with the sugar bound. Electron density to which no amino acid residue can be assigned and which could be the sugar molecule is within van der Waals distance of the sulfur atom.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jss.400060405
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