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.
Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-1392.
L L
LL
Ilag
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R
McKenna
M P
MP
Yadav
J N
JN
BeMiller
N L
NL
Incardona
M G
MG
Rossmann
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