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PDBsum entry 1box
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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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Contribution of a conserved asparagine to the conformational stability of ribonucleases sa, Ba, And t1.
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Authors
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E.J.Hebert,
A.Giletto,
J.Sevcik,
L.Urbanikova,
K.S.Wilson,
Z.Dauter,
C.N.Pace.
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Ref.
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Biochemistry, 1998,
37,
16192-16200.
[DOI no: ]
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PubMed id
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Abstract
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The contribution of hydrogen bonding by peptide groups to the conformational
stability of globular proteins was studied. One of the conserved residues in the
microbial ribonuclease (RNase) family is an asparagine at position 39 in RNase
Sa, 44 in RNase T1, and 58 in RNase Ba (barnase). The amide group of this
asparagine is buried and forms two similar intramolecular hydrogen bonds with a
neighboring peptide group to anchor a loop on the surface of all three proteins.
Thus, it is a good model for the hydrogen bonding of peptide groups. When the
conserved asparagine is replaced with alanine, the decrease in the stability of
the mutant proteins is 2.2 (Sa), 1.8 (T1), and 2.7 (Ba) kcal/mol. When the
conserved asparagine is replaced by aspartate, the stability of the mutant
proteins decreases by 1.5 and 1.8 kcal/mol for RNases Sa and T1, respectively,
but increases by 0.5 kcal/mol for RNase Ba. When the conserved asparagine was
replaced by serine, the stability of the mutant proteins was decreased by 2.3
and 1.7 kcal/mol for RNases Sa and T1, respectively. The structure of the Asn 39
--> Ser mutant of RNase Sa was determined at 1.7 A resolution. There is a
significant conformational change near the site of the mutation: (1) the side
chain of Ser 39 is oriented differently than that of Asn 39 and forms hydrogen
bonds with two conserved water molecules; (2) the peptide bond of Ser 42 changes
conformation in the mutant so that the side chain forms three new intramolecular
hydrogen bonds with the backbone to replace three hydrogen bonds to water
molecules present in the wild-type structure; and (3) the loss of the anchoring
hydrogen bonds makes the surface loop more flexible in the mutant than it is in
wild-type RNase Sa. The results show that burial and hydrogen bonding of the
conserved asparagine make a large contribution to microbial RNase stability and
emphasize the importance of structural information in interpreting stability
studies of mutant proteins.
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