Sperm microtubule inner protein 9 (SPMIP9)

Sperm microtubule inner protein 9 (SPMIP9) is a highly conserved structural protein found on the inner surfaces of doublet and singlet microtubules in mammalian sperm flagella and other motile cilia[1][4][3]. SPMIP9 forms characteristic periodic striations or spiral complexes (known as TAILS in the sperm flagellar singlet microtubules), providing stabilization and possibly protecting against external stress[1]. In ciliary doublet microtubules, SPMIP9 creates distinctive 8-nm repeating striations, binding between alpha- and beta-tubulin dimers and contributing to microtubule lattice stability[1][3]. The SPMIP9 fold is unique among human proteins, consisting of an eight-helix bundle[1]. While its full physiological role is unclear, loss or alteration could theoretically impair sperm motility or ciliary function, implicating a role in male fertility or in diseases involving motile cilia, but there are currently no direct disease or drug associations[2][4][6]. SPMIP9 is not a receptor, enzyme, pharmacological target, or biomarker.

Other names

C2orf51TEX37TSC21FLJ25369Testis-expressed sequence 37 proteinTestis-specific conserved protein of 21 kDaTestis-Specific Conserved gene 21kDaprotein SPMIP9protein TSC21testis expressed 37Sperm acrosome-associated protein 9 (SPACA9)

Not applicable