- Mona/Gads SH3C binding to hematopoietic progenitor kinase 1 (HPK1) combines an atypical SH3 binding motif, R/KXXK, with a classical PXXP motif embedded in a polyproline type II (PPII) helix. Lewitzky, M., Harkiolaki, M., Domart, M.C., Jones, E.Y., Feller, S.M. J. Biol. Chem. (2004)