| First Author | Ulke-Lemée A | Year | 2014 |
| Journal | Biochim Biophys Acta | Volume | 1844 |
| Issue | 9 | Pages | 1580-90 |
| PubMed ID | 24905744 | Mgi Jnum | J:217956 |
| Mgi Id | MGI:5616279 | Doi | 10.1016/j.bbapap.2014.05.011 |
| Citation | Ulke-Lemee A, et al. (2014) Two domains of the smoothelin-like 1 protein bind apo- and calcium-calmodulin independently. Biochim Biophys Acta 1844(9):1580-90 |
| abstractText | The smoothelin-like 1 protein (SMTNL1) is a modulator of smooth and skeletal muscle contractility and can bind to calmodulin and tropomyosin. Calmodulin is the major calcium sensor of eukaryotic cells and it can cycle between calcium-free (apo-CaM) and calcium-bound (Ca-CaM) forms. Bioinformatic screening of the SMTNL1 sequence predicted a second CaM-binding region (CBD1) that is located N-terminal to the previously defined apo-CaM-binding site (CBD2). Pull-down assays, surface plasmon resonance, isothermal calorimetry and NMR techniques were used to determine that CBD1 associated preferentially to Ca-CaM while CBD2 bound preferentially to apo-CaM. Mutation of hydrophobic residues abolished Ca-CaM-binding to CBD1 while acidic residues in CBD2 were necessary for apo-CaM-binding to CBD2. The dissociation constant (Kd) for Ca-CaM-binding to a CBD1 peptide was 26 *10(-6)M while the value for binding to a longer protein construct was 0.5 *10(-6)M. The binding of SMTNL1 to both apo-CaM and Ca-CaM suggests that endogenous CaM is continuously associated with SMTNL1 to allow for quick response to changes in intracellular calcium levels. We also found that the intrinsically disordered N-terminus of SMTNL1 can reduce binding to apo-CaM and increase binding to Ca-CaM. This finding suggests that an additional CaM-binding region may exist and/or that intramolecular interactions between the N-terminus and the folded C-terminus reduce apo-CaM-binding to CBD2. Intriguingly, CBD1 is located close to the SMTNL1 phosphorylation site and tropomyosin-binding region. We discuss the possibility that all three signals are integrated at the region surrounding CBD1. |
