Journal:JBIC:3
From Proteopedia
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Structural characterization of human S100A16, a low-affinity calcium binder
Elena Babini • Ivano Bertini • Valentina Borsi • Vito Calderone • Xiaoyu Hu • Claudio Luchinat • Giacomo Parigi[1]
Molecular Tour
S100A16 is a special S100 member because it does not perform a significant conformational change upon calcium(II) binding. This was observed after determination of the solution structures of apo and calcium(II)-bound S100A16 and the crystal structure of apo S100A16. The likely reason is the lower calcium binding affinity and stronger hydrophobic interaction between helix III and IV present in this protein with respect to other S100 proteins. Another characteristic of S100A16 is that the helix IV has the same length in both apo and calcium(II) forms because of the presence of a Gly-Gly-Ile-Thr-Gly-Pro sequence motif. 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. Calcium binding was proved by both NMR titration and Isothermal Titration Calorimetry (ITC) experiments. Even if the important Glu residue in the last position of first EF-hand calcium binding loop is missing, these experimental data indicated that S100A16 can still bind one calcium(II) ion in such loop. NMR relaxation studies showed that the first calcium binding loop and the beginning of the second helix are the most flexible regions in both the apo and calcium(II)-bound S100A16. Although the biological function of S100A16 is still unclear yet, these structural and dynamic properties can provide useful information for further functional studies.
