Carboxyl Terminus of HOATZ is Intrinsically Disordered and Interacts with Heat Shock Protein A Families

Hoatz is a vertebrate-specific gene, the defects of which result in hydrocephalus and oligo-astheno-teratozoospermia in mice. It encodes a 19-kDa protein lacking any domains of known function.To understand the protein activity, we purified the carboxyl-terminal fragment that is conserved among different species, and analyzed its structure and potential binding proteins. A soluble 9.9-kDa HOATZ fragment, including a poly-histidine tag (designated HOATZ-C), was purified to homogeneity.The gel filtration profile and circular dichroism spectra collectively indicated that HOATZ-C was intrinsically disordered. When HOATZ-C was mixed with cleared lysate from Hoatz-null mouse testis, several proteins, including two of ~70 kDa size, were specifically co-purified with HOATZ-C on a nickel column.Based on the peptide mass fingerprinting of these bands, two members of the heat-shock protein family A were identified. These data may indicate the role of HOATZ in stress regulation in cells characterized by motile cilia and flagella.