Journal:JBIC:3

=== Structural characterization of human S100A16, a low-affinity calcium binder ===

=== Structural characterization of human S100A16, a low-affinity calcium binder ===

<big>Elena Babini • Ivano Bertini • Valentina Borsi • Vito Calderone • Xiaoyu Hu • Claudio Luchinat • Giacomo Parigi</big><ref >DOI 10.1007/s00775-010-0721-3</ref>

<big>Elena Babini • Ivano Bertini • Valentina Borsi • Vito Calderone • Xiaoyu Hu • Claudio Luchinat • Giacomo Parigi</big><ref >DOI 10.1007/s00775-010-0721-3</ref>

S100A16 is a special member of the S100 class of calcium binding proteins, because it <scene name='Journal:JBIC:3/As/12'>performs a conformational change upon calcium(II) binding</scene> much smaller than experienced by most S100 proteins. This was observed after determination of the solution structures of apo and <scene name='Journal:JBIC:3/Dual_binding_calcium/3'>calcium(II)-bound S100A16</scene> and the <scene name='Journal:JBIC:3/Crysal/2'>crystal structure of apo S100A16</scene>. The likely reason for minimal conformational change <scene name='Journal:JBIC:3/Calcium_binding_start/7'>in S100A16</scene> is the lower calcium binding affinity and stronger <scene name='Journal:JBIC:3/Hydrophobic_interactions_2/3'>hydrophobic interaction</scene> between <scene name='Journal:JBIC:3/Please_work/3'>helix III and IV present in this protein </scene> with respect to other S100 proteins. Another characteristic of <scene name='Journal:JBIC:3/Opening/3'>S100A16</scene> is that the helix IV has the same length in <scene name='Journal:JBIC:3/25_residue_long_apo/3'>both apo</scene> and <scene name='Journal:JBIC:3/25_residue_calclium_bound/3'>calcium(II) forms</scene> because of <scene name='Journal:JBIC:3/Motif_good/5'>the presence of a Gly-Gly-Ile-Thr-Gly-Pro sequence motif</scene> in helix IV. Based on the available structures of S100 members, we analyzed and summarized all their conformational changes due to calcium(II) binding by a principal component analysis. <scene name='Journal:JBIC:3/Calcium_binding_start/7'>Calcium binding</scene> was proved by both NMR titration and Isothermal Titration Calorimetry (ITC) experiments. Even if the <scene name='Journal:JBIC:3/Binding_calcium_glu/2'>important Glu residue</scene> in the last position of first EF-hand calcium binding loop <scene name='Journal:JBIC:3/Binding_calcium/13'>is missing</scene>, these experimental data indicated that S100A16 can still bind one calcium(II) ion in such loop. NMR relaxation <scene name='Journal:JBIC:3/Flexible_broadwide/4'>studies showed that the first calcium binding loop and the beginning of the second helix</scene> are the most <scene name='Journal:JBIC:3/Flexible_broad/3'>flexible regions in both the apo and calcium(II)-bound S100A16</scene>. Although the biological function of S100A16 is still unclear yet, these structural and dynamic properties can provide useful information for further functional studies.

S100A16 is a special member of the S100 class of calcium binding proteins, because it <scene name='Journal:JBIC:3/As/12'>performs a conformational change upon calcium(II) binding</scene> much smaller than experienced by most S100 proteins. This was observed after determination of the solution structures of apo and <scene name='Journal:JBIC:3/Dual_binding_calcium/3'>calcium(II)-bound S100A16</scene> and the <scene name='Journal:JBIC:3/Crysal/2'>crystal structure of apo S100A16</scene>. The likely reason for minimal conformational change <scene name='Journal:JBIC:3/Calcium_binding_start/7'>in S100A16</scene> is the lower calcium binding affinity and stronger <scene name='Journal:JBIC:3/Hydrophobic_interactions_2/3'>hydrophobic interaction</scene> between <scene name='Journal:JBIC:3/Please_work/3'>helix III and IV present in this protein </scene> with respect to other S100 proteins. Another characteristic of <scene name='Journal:JBIC:3/Opening/3'>S100A16</scene> is that the helix IV has the same length in <scene name='Journal:JBIC:3/25_residue_long_apo/3'>both apo</scene> and <scene name='Journal:JBIC:3/25_residue_calclium_bound/3'>calcium(II) forms</scene> because of <scene name='Journal:JBIC:3/Motif_good/5'>the presence of a Gly-Gly-Ile-Thr-Gly-Pro sequence motif</scene> in helix IV. Based on the available structures of S100 members, we analyzed and summarized all their conformational changes due to calcium(II) binding by a principal component analysis. <scene name='Journal:JBIC:3/Calcium_binding_start/7'>Calcium binding</scene> was proved by both NMR titration and Isothermal Titration Calorimetry (ITC) experiments. Even if the <scene name='Journal:JBIC:3/Binding_calcium_glu/2'>important Glu residue</scene> in the last position of first EF-hand calcium binding loop <scene name='Journal:JBIC:3/Binding_calcium/13'>is missing</scene>, these experimental data indicated that S100A16 can still bind one calcium(II) ion in such loop. NMR relaxation <scene name='Journal:JBIC:3/Flexible_broadwide/4'>studies showed that the first calcium binding loop and the beginning of the second helix</scene> are the most <scene name='Journal:JBIC:3/Flexible_broad/3'>flexible regions in both the apo and calcium(II)-bound S100A16</scene>. Although the biological function of S100A16 is still unclear yet, these structural and dynamic properties can provide useful information for further functional studies.

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