SPRED1 (Sprouty-related protein with an EVH1 domain-1) is a 55 kDa member of the SPRED family of regulatory molecules. It inhibits mitogenic signaling by blocking Ras activation of Raf, and disrupts actin stress fiber formation by binding TESK1. Human SPRED1 is 444 amino acids (aa) in length. It contains an N-terminal WH1/EVH1 domain that is involved in ERK inhibition (aa 6 - 123), a central KBD domain that binds to the SCFR (aa 233 - 285), and a C-terminal Cys-rich/Sprouty-related domain that mediates homo- and heterodimerization with SPRED2, binding to TESK1, and undergoes palmitoylation for membrane localization (aa 334 - 442). There is one splice variant that shows a nine Lys substitution for aa 269 - 444.