※ WW family introduction

    WW domains are signaling modules of approximately 40 amino acids that fold into three anti-parallel β strands and bind short proline-rich sequences, predominantly composed of PPXY, PPLP or PPR motifs. It is frequently associated with other domains typical for proteins in signal transduction processes. The proline isomerase Pin1 and the ubiquitin ligase Nedd4, however, contain WW domains that specifically recognize pSer–Pro and pThr–Pro motifs (1).

Reference
1. Yaffe, M.B. (2001) Phosphoserine/threonine-binding domains . Curr Opin Cell Biol, 13, 131-8. PMID: 11248545