Structure of a human clara cell dhospholipid-binding protein- igand complex at 1.9 å resolution

The Clara cell phospholipid-binding protein, previously referred to as CC10, is a homodimeric protein of Mr 15,800. It is secreted into the bronchioalveolar lining layer in mammalian lung. A combination of X-ray crystallography and chemical analysis was used to determine that phosphatidylcholine and phophatidylinositol are bound to the protein as isolated from human lung lavage. We now report the crystal structure of the protein-phospholipid complex at 1.9 A resolution. The phospholipid is bound inside the protein's large hydrophobic cavity. A model is proposed for the manner in which a channel may open to provide access to the cavity, allowing the binding or potential release of phospholipid.