Calcium ion-induced structural changes in bacteriophage phi X174.
Monoclinic P2(1) crystals of the bacteriophage phi X174 have been incubated with calcium ions (Ca2+) and the induced structural conformational changes studied to 3 A resolution with X-ray crystallographic methods. Three different types of Ca2+ binding sites have been located within the asymmetric unit of the virion. Two sets of sites are associated with the F capsid protein. One set of sites associated with the F protein is in a general position near the icosahedral 3-fold axes of the virus, with the main-chain carbonyl oxygen atoms of residues Gly1321, Asp1421, Met1424 and Ser1426, and the side-chains of Gln1004 and Asp1421 as ligands. The other set of sites associated with the F protein is on the icosahedral 3-fold axes, with the symmetry-related main-chain carbonyl oxygen atoms of Ser1001 and the side-chains of Asn1002 as ligands. The bound Ca2+ induce a conformational change of the amino-terminal residues of the F proteins. A third set of sites, consisting of a pair of Ca2+ on the icosahedral 5-fold axes, are associated with the G spike protein and are concurrently liganded by the symmetry-related carbonyl oxygen side-chains of Asp2117. Concomitant with the binding of Ca2+ to the phage is the rotation of the Asp1209 side-chain of the F protein towards some additional electron density that was not observed in the absence of Ca2+. This density is situated in a shallow depression near the icosahedral 2-fold axes of the virus, and has been tentatively interpreted as a bound glucose molecule that is ordered only in the presence of Ca2+. The putative glucose binding site may be related to the attachment of the virus to cell surface lipopolysaccharides in the initial stages of Escherichia coli infection.
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Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-1392.
McKenna
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Yadav
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BeMiller
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Incardona
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Rossmann
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D000595:Amino Acid Sequence; D010584:Bacteriophage phi X 174 / Q000187:drug effects / Q000648:ultrastructure*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D018360:Crystallography, X-Ray; D005947:Glucose / Q000378:metabolism; D007525:Isoelectric Focusing; D008969:Molecular Sequence Data; D011487:Protein Conformation; D014764:Viral Proteins / Q000378:metabolism
D014764:Viral Proteins; D005947:Glucose; D002118:Calcium