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PDBsum entry 1mh3
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Sugar binding, DNA binding protein
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PDB id
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1mh3
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Insights into binding cooperativity of mata1/matalpha2 from the crystal structure of a mata1 homeodomain-Maltose binding protein chimera.
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Authors
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A.Ke,
C.Wolberger.
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Ref.
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Protein Sci, 2003,
12,
306-312.
[DOI no: ]
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PubMed id
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Abstract
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The Yeast MATa1 and MATalpha2 are homeodomain proteins that bind DNA
cooperatively to repress transcription of cell type specific genes. The DNA
affinity and specificity of MATa1 in the absence of MATalpha2, however, is very
low. MATa1 is converted to a higher affinity DNA-binding protein by its
interaction with the C-terminal tail of MATalpha2. To understand why MATa1 binds
DNA weakly by itself, and how the MATalpha2 tail affects the affinity of MATa1
for DNA, we determined the crystal structure of a maltose-binding protein
(MBP)-a1 chimera whose DNA binding behavior is similar to MATa1. The overall
MATa1 conformation in the MBP-a1 structure, which was determined in the absence
of alpha2 and DNA, is similar to that in the a1/alpha2/DNA structure. The sole
difference is in the C-terminal portion of the DNA recognition helix of MATa1,
which is flexible in the present structure. However, these residues are not in a
location likely to be affected by binding of the MATalpha2 tail. The results
argue against conformational changes in a1 induced by the tail of MATalpha2,
suggesting instead that the MATalpha2 tail energetically couples the DNA binding
of MATalpha2 and MATa1.
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Figure 1.
Figure 1. Overview of the crystal structure of the a1/  2/DNA ternary
complex. The a1 homeodomain is shown in red, 2 in blue, and
the DNA in silver. The three helices of a1 and the tail of 2 have been
noted. The 2 tail folds
into a short amphipathic helix and packs against the groove
formed by Helix 1 and 2 of a1.
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Figure 2.
Figure 2. Overview of the MBP-a1 chimeric protein
structure. The MBP moiety is shown in cyan; the five-residue
polyalanine linker and the a1 homeodomain are shown in magenta.
Note the short alanine linker that adopts a turn conformation to
avoid steric clashes between a1 and MBP molecule. The 2 tail binding
site on the a1 homeodomain is not in contact with MBP.
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The above figures are
reprinted
by permission from the Protein Society:
Protein Sci
(2003,
12,
306-312)
copyright 2003.
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