B9 domain-containing protein 1 (B9D1)

B9 domain-containing protein 1 (B9D1) is a soluble protein localized to the ciliary transition zone (TZ) in eukaryotic cells. It forms a tripartite complex with MKS1 and B9D2—these B9 domain proteins have essential, interdependent roles in establishing a diffusion barrier at the TZ that controls the movement of membrane proteins into the ciliary compartment[1][2]. This complex is not strictly required for the overall permeability barrier, as trafficking of intraflagellar transport (IFT) particles remains unaffected in knockout models, but it is critical for correct membrane protein composition and mild defects in ciliogenesis are observed in the absence of B9D1 or its complex partners[1][2]. Defective B9D1 function has been implicated in human ciliopathies such as Meckel syndrome and Joubert syndrome (notably, MKS9 is an alias for B9D1 in the context of Meckel syndrome)[1][2]. B9D1 is not recognized as a direct therapeutic target, with no known interacting drugs, mechanisms of drug action, or use as a clinical biomarker as of current data[1][2]. If further disease-specific or clinical biomarker information is required, genetic studies could be considered, but present data establish its primary biological role in ciliary membrane compartmentalization rather than as a tractable therapeutic target[1][2].

Other names

B9D1MKSR1B9EPPB9MKS9MKSR-1MKS1-related protein 1Endothelial precursor protein B9JBTS27