This domain, predominantly found in lung surfactant protein D, forms a triple-helical parallel coiled coil, and mediates trimerisation of the protein [1].

1: Solution structure of the coiled-coil trimerization domain from lung surfactant protein D. Kovacs H, O'Ddonoghue SI, Hoppe HJ, Comfort D, Reid KB, Campbell D, Nilges M; J Biomol NMR. 2002;24:89-102. PMID:12495025