Díaz-Casas, Adalberto

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    Thermodynamics governing binding of Homo sapiens centrin – Homo sapiens Sfi1p21 Complexes
    (2012) Díaz-Casas, Adalberto; Pastrana-Ríos, Belinda; College of Arts and Sciences - Sciences; Meléndez, Enrique; Ríos, Robert; Department of Chemistry; Sundaram, Paul
    Centrin is a member of the EF-hand superfamily of calcium-binding proteins and has a molecular weight of ~20 kDa. In Homo sapiens, four centrin isoforms have been determined: centrin 1 (Hscen1), which is found in male germ cells, certain neurons and ciliated cells, centrin 2 (Hscen2) and centrin 3 (Hscen3) are expressed in all somatic cells, and centrin 4 (Hscen4) found in neurons. We focused our research on Sfi1, a centrin binding protein of 1242 amino acids and comprising 23 tandem centrin-binding sites (CBS). Specifically, we studied a soluble Sfi1 peptide comprised of the 21st centrin binding site (HsSfi1p21). HsSfi1p21 exhibits the hydrophobic triad (W1L4L8) which is found to be essential for the interaction between centrin and its biological targets. Using isothermal titration calorimetry, the interaction between Hscen1 and HsSfi1p21 was analyzed at 25°C, 30°C, 35°C, and 40°C. At 35°C, the complex shows the highest stability (ΔG = -10.2 kcal/mol) and affinity (Ka = 1.7 x 107 M -1 ) with a favorable enthalpy (ΔH = -29.0 kcal/mol) and unfavorable entropy (-TΔS = 18.8 kcal/mol). By a comparative thermodynamic analysis of the interaction of three human centrin isoforms (Hscen1, Hscen2, and Hscen3) with HsSfi1 at 30°C, we found that Hscen3-HsSfi1p21 complex presented the highest stability and affinity interaction. From these results, we found that the stability on centrin-Sfi1p complex is dependent to the relative stability of centrin.