Binding properties and structural predictions of homeodomain proteins CDX1/2 and HOXD8

Abstract

Human CDX1 and CDX2 genes play important roles in the regulation of cell proliferation and differentiation in the intestine. Hox genes clustered on four chromosomal regions (A-D) specify positional signaling along the anterior-posterior body axis, including intestinal development. Using glutathione S-transferase (GST) pulldown assays, molecular interaction measurements, and fluorescence measurements, we found that the homeodomains (HDs) of CDX1 and CDX2 directly interact with that of HOXD8 in vitro. CDX1 showed significant affinity for HOXD8, but CDX2 showed weak affinity for HOXD8. Thus far, three-dimensional structures of CDX1/2 and HOXD8 have not been determined. In this study, we developed a molecular docking model by homology modeling based on the structures of other HD members. Proteins with mutations in the HD of CDX1 (S185A, N190A, T194A, and V212A) also bound to the HD of HOXD8. Our study suggests that the HDs of CDX1/2 resemble those of HOXD8, and we provide the first insight into the interaction between the HDs of CDX1/2 proteins and those of HOXD8.