Ca2+ stabilises the CRDs of CL-K1. A) Fluorescence spectra of the CL-K1 fragment in different buffers. The λex was 280 nm. B) Ca2+ binding to the CL-K1 fragment measured by fluorescence. Measurements were recorded at an λem of 345 nm. C) Urea denaturation in the presence and absence of Ca2+ (2 mM). D) Proteolysis of CL-K1 in the presence of increasing concentrations of Ca2+ (two fold dilutions starting at 5 mM). Samples were separated by SDS-PAGE and gels were scanned to determine the amount of CL-K1 remaining. The amount of trypsin was 0.5% (w/w). The intensities of bands corresponding to the neck and CRD and the CRD alone were combined. A sample gel is shown in F). E) Proteolysis of CL-K1 in the presence and absence of Ca2+. Two fold serial dilutions of trypsin were used at a starting concentration of 2% (w/w). In all experiments data are mean ± error from two separate experiments. CL-K1, collectin-K1; CRD, carbohydrate-recognition domain.