1goc
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(New page: 200px<br /><applet load="1goc" size="450" color="white" frame="true" align="right" spinBox="true" caption="1goc, resolution 2.0Å" /> '''COOPERATIVE STABILIZA...)
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Revision as of 14:04, 20 November 2007
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COOPERATIVE STABILIZATION OF ESCHERICHIA COLI RIBONUCLEASE HI BY INSERTION OF GLY-80B AND GLY-77-> ALA SUBSTITUTION
Overview
The insertion of a Gly residue (designated as Gly-80b) between the C-cap, of the alpha II-helix (Gln-80) and the N-cap of the alpha III-helix, (Trp-81) in Escherichia coli ribonuclease HI enhances the protein, stability by 0.4 kcal/mol in delta G (Kimura, S., Nakamura, H., Hashimoto, T., Oobatake, M., & Kanaya, S. (1992) J. Biol. Chem. 267, 21535-21542)., Another mutation within the alpha II-helix, Gly-77-->Ala, reduces the, stability by 0.9 kcal/mol. Simultaneous introduction of these mutations, enhances the stability by 0.8 kcal/mol, indicating that the effects of, these mutations are cooperative and not simply independent. We determined, the crystal structures of these three mutant proteins (G80b-, A77-, and, A77/G80b-RNase H) to investigate this cooperative mechanism of the protein, stabilization. The structures revealed that the inserted Gly-80b assumes a, left-handed helical conformation in both the G80b- and the A77/G80b-RNase, H. This inserted glycine residue allows the formation of a "paperclip", which is a common motif at the C-termini of alpha-helices. Accompanying, the formation of the paperclip motif, two intrahelical hydrogen bonds are, formed between the backbone atoms (O78-N80b and O80b-N84). The, stabilization caused by the insertion of Gly-80b can be ascribed to the, formation of these hydrogen bonds. The Gly-77-->Ala substitution, destabilizes the protein due to the deformed packing interactions in the, hydrophobic core around Ala-77 and the stress in the wedged indole ring of, Trp-81. These effects are alleviated by the insertion of Gly-80b, which, relaxes the backbone structure.(ABSTRACT TRUNCATED AT 250 WORDS)
About this Structure
1GOC is a Single protein structure of sequence from Escherichia coli. Active as Ribonuclease H, with EC number 3.1.26.4 Full crystallographic information is available from OCA.
Reference
Cooperative stabilization of Escherichia coli ribonuclease HI by insertion of Gly-80b and Gly-77-->Ala substitution., Ishikawa K, Nakamura H, Morikawa K, Kimura S, Kanaya S, Biochemistry. 1993 Jul 20;32(28):7136-42. PMID:8393706
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