Sperm surface protein Sp17 is a protein present at the cell surface. The N-terminus has sequence similarity to human cAMP-dependent protein kinase A (PKA) type II alpha regulatory subunit (RIIa) while the C-terminus has an IQ calmodulin-binding motif. The central portion of the protein has carbohydrate binding motifs and likely functions in cell-cell adhesion.

The protein was initially characterized by its involvement in the binding of sperm to the zona pellucida of the oocyte. Recent studies indicate that it is also involved in additional cell-cell adhesion functions such as immune cell migration and metastasis. A retrotransposed pseudogene is present on chromosome 10q22.