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PDBsum entry 3so0
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Metal binding protein
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PDB id
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3so0
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Contents |
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(+ 1 more)
86 a.a.
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72 a.a.
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References listed in PDB file
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Key reference
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Title
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Decoding the molecular design principles underlying ca(2+) binding to βγ-Crystallin motifs.
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Authors
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A.Mishra,
S.K.Suman,
S.S.Srivastava,
R.Sankaranarayanan,
Y.Sharma.
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Ref.
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J Mol Biol, 2012,
415,
75-91.
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PubMed id
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Abstract
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Numerous proteins belonging to the recently expanded βγ-crystallin superfamily
bind Ca(2+) at the double-clamp N/D-N/D-X(1)-X(2)-S/T-S motif. However, there
have been no attempts to understand the intricacies involving Ca(2+) binding,
such as the determinants of Ca(2+)-binding affinity and their contributions to
gain in stability. This work is an in-depth analysis of understanding the modes
and determinants of Ca(2+) binding to βγ-crystallin motifs. We have performed
extensive naturally occurring substitutions from related proteins on the
βγ-crystallin domains of flavollin, a low-affinity Ca(2+)-binding protein, and
clostrillin, a moderate-affinity protein. We monitored the consequences of these
modifications on Ca(2)(+) binding by isothermal titration calorimetry, thermal
stability and conformational and crystal structure analyses. We demonstrate that
Ca(2)(+) binding to the two sites of a βγ-domain is interdependent and that
the presence of Arg at the fifth position disables a site. A change from Thr to
Ser, or vice versa, influences Ca(2+)-binding affinity, highlighting the basis
of diversity found in these domains. A subtle change in the first site has a
greater influence on Ca(2)(+) binding than a similar alteration in the second
site. Thus, the second site is more variable in nature. Replacing an acidic or
hydrophobic residue in a binding site alters the Ca(2+)-binding properties
drastically. While it appears from their binding site sequence that these
domains have evolved randomly, our examination illustrates the subtlety in the
design of these modules. Decoding such design schemes would aid in our
understanding of the functional themes underlying differential Ca(2)(+) binding
and in predicting these in emerging sequence information.
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